Optical film, optical compensation film, polarizing plate and liquid crystal display

ABSTRACT

An optical film is provided and has retardations satisfying relations (1) to (3): 
       0≦Re(550)≦10;  (1)
 
       −25≦Rth(550)≦25; and  (2)
 
       |I|+|II|+|III|+|IV|&gt;0.5 (nm),  (3)
 
     with definitions: 
     I=Re(450)-Re(550); 
     II=Re(650)-Re(550); 
     III=Rth(450)-Rth(550); and 
     IV=Rth(650)-Rth(550), 
     wherein Re(450), Re(550) and Re(650) are in-plane retardations measured with lights of wavelength of 450, 550 and 650 nm, respectively; and Rth(450), Rth(550) and Rth(650) are retardations in a thickness direction of the optical film, which are measured with lights of wavelength of 450, 550 and 650 nm, respectively.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/515,783,filed Sep. 6, 2006, which in turn claims priority to JapaneseApplication Nos. 2005-262304 and 2006-63026, filed Sep. 9, 2005 and Mar.8, 2006, the entire content of each of which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to an optical film adapted for use in aliquid crystal display, and an optical material such as an opticalcompensation film or a polarizing plate, and a liquid crystal displayutilizing the same.

DESCRIPTION OF BACKGROUND ART

Liquid crystal displays are widely utilized for a monitor of a personalcomputer and a portable equipment, and for televisions, because ofvarious advantages such as a low voltage drive, a lower electric powerconsumption and possibility for a compactification and a thin structure.Such liquid crystal displays are proposed in various modes depending onthe liquid crystal molecules within a liquid crystal cell, but a TNmode, in which the liquid crystal molecules are twisted by about 90°from a lower substrate to an upper substrate of the liquid crystal cell,has been employed principally.

In general, the liquid crystal display is constituted of a liquidcrystal cell, an optical compensation sheet, and a polarizer. Theoptical compensation sheet is used for removing a coloration on theimage or expanding a view angle, and a stretched birefringent film or atransparent film coated with a liquid crystal material is used for thispurpose. For example JP-A-62-210423 discloses a technology of applyingan optical compensation film, which is prepared by coating, aligning andfixing a discotic liquid crystal on a triacetyl cellulose film, to aTN-mode liquid crystal cell, thereby expanding a viewing angle. However,a liquid crystal display for a television use, having a large image sizeand anticipated for observation from various angles, involves strictrequirements for the viewing angle dependence of the image, and even theaforementioned method is unable to meet such requirements. For thisreason, liquid crystal displays different from the TN mode are beinginvestigated, such as those of an IPS (in-plane switching) mode, an OCB(optically compensatory bend) mode and a VA (vertically aligned) mode.In particular, the VA mode is attracting attention for use intelevision, because of a high contrast and a relatively high productionyield.

However the VA mode, though being capable of displaying an almostcomplete black color in a normal direction to the panel, causes a lightleakage when the panel is observed from an inclined direction, and thusresults in a limited viewing angle. In order to avoid such drawback, itis proposed to position a retardation plate, having a refractive indexanisotropy in which a refractive index in a film thickness direction issufficiently smaller than a refractive index in an in-plane direction,between the liquid crystal layer and at least one of the polarizingplates (for example JP-A-62-210423). It is also proposed to reduce thelight leakage, by utilizing, in combination, a first retardation platehaving a positive monoaxial refractive index anisotropy and a secondretardation plate having a negative refractive index anisotropy in whichthe refractive index in the film thickness direction is sufficientlysmaller than the refractive index in the in-plane direction (for exampleJapanese Patent No. 3027805). It is further proposed to improve theviewing angle characteristics of a VA-mode liquid crystal display,utilizing an optically biaxial retardation plate, having refractiveindexes different in three-dimensional directions of a film (for exampleJapanese Patent No. 3330574).

On the other hand, also in the IPS mode, a slight light leakage in adiagonally inclined incident direction in a black display state isrecognized as a cause of deterioration in the display quality. Forimproving the displayed color and the viewing angle in the black displaystate, it is being considered, also in the IPS mode, to provide anoptical compensation material with birefringent characteristics, betweenthe liquid crystal layer and the polarizing plate. It is disclosed, forexample, that the coloration of the image, when a white display or adisplay of an intermediate tone is observed from an inclined direction,can be improved by positioning a birefringent medium, having mutuallyorthogonal optical axes and capable of compensating a change in theretardation of the liquid crystal layer in an inclined position, betweena substrate and a polarizing plate (see JP-A-9-80424). There are alsodisclosed a method of utilizing an optical compensation film, formed bya styrenic polymer or a discotic liquid crystalline compound, having anegative intrinsic birefringence (see JP-A-10-54982, JP-A-11-202323 andJP-A-9-292522), a method of combining, as an optical compensation film,a film having a positive birefringence and having an optical axis in theplane of the film and a film having a positive birefringence and havingan optical axis in a normal direction to the film (see JP-A-11-133408),a method of utilizing a biaxial optical compensation sheet with aretardation of a half wavelength (see JP-A-11-305217), and a method ofutilizing a film having a negative retardation as a protective film of apolarizing plate and providing a surface of such film with an opticalcompensation layer having a positive retardation (see JP-A-10-307291).Also disclosed is an invention of utilizing a retardation film having Nzof from 0.4 to 0.6 and an in-plane retardation of from 200 to 350 nmthereby suppressing a light leakage, caused by an aberration in acrossing angle of the polarizing axes from an orthogonal relationship,experienced when orthogonally disposed polarizing plates are observedfrom an inclined direction (see JP-A-2004-4642).

However, the aforementioned methods reduces the light leakage only in acertain wavelength region (for example green light around 550 nm), anddo not take into consideration the light leakage in other wavelengthregions (for example blue light around 450 nm and red light around 650nm). Therefore, so-called color shift phenomenon, in which a blackdisplay is colored blue or red when observed from an inclined direction,has not been resolved.

SUMMARY OF THE INVENTION

An object of an illustrative, non-limiting embodiment of the inventionis to provide an optical film, having a high contrast ratio over a widerange and capable of suppressing a color shift (color shift whenobserved from an inclined direction), and to provide an optical materialsuch as an optical compensation film or a polarizing plate and a liquidcrystal display, utilizing such optical film.

The above-mentioned object can be accomplished by following means.

1. An optical film having retardations satisfying relations (1) to (3):

0≦Re(550)≦10;  (1)

−25≦Rth(550)≦25; and  (2)

|I|+|II|+|III|+|IV|>0.5 (nm),  (3)

with definitions:

I=Re(450)-Re(550);

II=Re(650)-Re(550);

III=Rth(450)-Rth(550); and

IV=Rth(650)-Rth(550),

wherein Re(450), Re(550) and Re(650) are in-plane retardations measuredwith lights of wavelength of 450, 550 and 650 nm, respectively; andRth(450), Rth(550) and Rth(650) are retardations in a thicknessdirection of the optical film, which are measured with lights ofwavelength of 450, 550 and 650 nm, respectively.2. The optical film according to the item 1, wherein I, II, III and IVsatisfy relations (4-A) to (7-A):

−50≦I≦0;  (4-A)

0≦II≦50;  (5-A)

−50≦III<0; and  (6-A)

0<IV≦50.  (7-A)

3. The optical film according to the item 1, wherein I, II, III and IVsatisfy relations (4-B) to (7-B):

−50≦I<0;  (4-B)

0<II≦50;  (5-B)

0≦III≦50; and  (6-B)

−50≦IV≦0.  (7-B)

4. The optical film according to the item 1, wherein I, II, III and IVsatisfy relations (4-C) to (7-C):

0≦I≦50;  (4-C)

−50≦II≦0;  (5-C)

0<III≦50; and  (6-C)

−50≦IV<0.  (7-C)

5. The optical film according to the item 1, wherein I, II, III and IVsatisfy relations (4-D) to (7-D):

0<I≦50;  (4-D)

−50≦II<0;  (5-D)

−50≦III≦0; and  (6-D)

0≦IV≦50.  (7-D)

6. The optical film according to any one of the items 1 to 5, which isformed from a cellulose acylate a raw material polymer of the opticalfilm.7. The optical film according to the item 6, wherein the celluloseacylate has an acyl substituent, the acyl substituent is substantiallyonly an acetyl group, and a total substitution degree of the acylsubstituent is from 2.56 to 3.00.8. The optical film according to the item 6, wherein the celluloseacylate has an acyl substituent, the acyl substituent is substantiallyat least two of acetyl group, propionyl group and butanoyl group, and atotal substitution degree of the acyl substituent is from 2.50 to 3.00.9. The optical film according to any one of the items 1 to 8, whichcomprises a compound capable of reducing Rth(550) within a rangesatisfying relations (8) and (9):

(Rth(A)−Rth(0))/A≦−1.0; and  (8)

0.01≦A≦30,  (9)

wherein:

Rth(A) means Rth(nm) at 550 nm of the optical film containing thecompound capable of reducing Rth(550) by A %;

Rth(0) means Rth(nm) at 550 nm of the optical film not containing thecompound capable of reducing Rth(550); and

A means a weight % of the compound capable of reducing Rth(550) withrespect to a weight of a raw material polymer of the optical film, whichis taken as 100.

10. The optical film according to the items 1 to 9, which comprises acompound capable of increasing ΔRth, which is represented by a relation(10), within a range satisfying relations (11) and (12):

ΔRth=Rth(450)−Rth(650);  (10)

(ΔRth(B)−ΔRth(0))/B≧1.0; and  (11)

0.01≦B≦30,  (12)

wherein:

ΔRth(B) means ARth(nm) of the optical film containing the compoundcapable of increasing ΔRth by B %;

ΔRth(0) means ΔRth(nm) of thje optical film not containing the compoundcapable of increasing ΔRth; and

B means a weight (%) of the compound capable of increasing ΔRth withrespect to a weight of a raw material polymer of the optical film, whichis taken as 100.

11. The optical film according to the items 1 to 10, which has athickness of 20 to 200 μm.12. An optical compensation film comprising: an optical film accordingto any one of the items 1 to 11; and an optically anisotropic layersatisfying relations (13) and (14):

0≦Re≦400; and  (13)

−400≦Rth≦400,  (14)

wherein Re and Rth are an in-plane retardation and a retardation in athickness direction of the optically anisotropic layer, respectively,which are measured with a light having a wavelength within a visibleregion.13. The optical compensation film according to the item 12, wherein theoptically anisotropic layer contains a discotic liquid crystal.14. The optical compensation film according to the item 12 or 13,wherein the optically anisotropic layer contains a cholesteric liquidcrystal.15. The optical compensation film according to any one of the items 12to 14, wherein the optically anisotropic layer contains a rod-shapedliquid crystal.16. The optical compensation film according to any one of the items 12to 15, wherein the optically anisotropic layer contains a polymer film.17. The optical compensation film according to any one of the items 12to 16, wherein the polymer compound constituting the opticallyanisotropic layer contains at least a polymer material selected from thegroup consisting of polyamide, polyimide, polyester, polyether ketone,polyamidimide, polyesterimide, and polyarylether ketone.18. A polarizing plate comprising: a polarizer; and an optical filmaccording to any one of the items 1 to 11 or an optical compensationfilm according to any one of the items 12 to 17.19. A liquid crystal display comprising an optical film according to anyone of the items 1 to 11, at least one optical compensation filmaccording to any one of the items 12 to 17 or a polarizing plateaccording to the item 18.20. A liquid crystal display comprising: an optical film according toany one of the items 1 to 11, at least one optical compensation filmaccording to any one of the items 12 to 17 or a polarizing plateaccording to the item 18; and an optically anisotropic layer satisfyingrelations (15) and (16):

0≦Re≦400; and  (15)

−400≦Rth≦400,  (16)

wherein Re and Rth are an in-plane retardation and a retardation in athickness direction of the optically anisotropic layer, respectively,which are measured with a light having a wavelength within a visibleregion.21. The liquid crystal display according to the item 20, wherein theoptically anisotropic layer contains a discotic liquid crystal.22. The liquid crystal display according to the item 20 or 21, whereinthe optically anisotropic layer contains a cholesteric liquid crystal.23. The liquid crystal display according to any one of the items 20 to22, wherein the optically anisotropic layer contains a rod-shaped liquidcrystal.24. The liquid crystal display according to any one of the items 20 to23, wherein the optically anisotropic layer contains a polymer film.25. The liquid crystal display according to any one of the items 20 to24, wherein the polymer compound constituting the optically anisotropiclayer contains at least a polymer material selected from the groupconsisting of polyamide, polyimide, polyester, polyether ketone,polyamidimide, polyesterimide, and polyarylether ketone.26. The liquid crystal display according to any one of the items 19 to25, which further comprises a liquid crystal cell containing liquidcrystal molecules aligned in one of a vertical alignment, a parallelalignment and a bent alignment in a black display state of the liquidcrystal display.27. The liquid crystal display according to the item 26, wherein theliquid crystal molecules are aligned in the vertical alignment in theblack display state, and the liquid crystal display comprises anoptically anisotropic layer, the optically anisotropic layer including alayer satisfying relations (17) and (18):

10≦Re≦150; and  (17)

50≦Rth≦400,  (18)

wherein Re and Rth are an in-plane retardation and a retardation in athickness direction of the optically anisotropic layer, respectively,which are measured with a light having a wavelength within a visibleregion.28. The liquid crystal display according to the item 26, wherein theliquid crystal molecules are aligned in the parallel alignment in theblack display state, and the liquid crystal display comprises anoptically anisotropic layer, the optically anisotropic layer including alayer satisfying any one of relations from (19) to (22):

100≦Re≦400, and −50≦Rth≦50;  (19)

0≦Re≦20, and −400≦Rth≦−50;  (20)

60≦Re≦200, and 20≦Rth≦120; and  (21)

30≦Re≦150, and 100≦Rth≦400,  (22)

wherein Re and Rth are an in-plane retardation and a retardation in athickness direction of the optically anisotropic layer, respectively,which are measured with a light having a wavelength within a visibleregion.29. The liquid crystal display according to the item 26, wherein theliquid crystal molecules are aligned in the bent alignment in the blackdisplay state, and the liquid crystal display comprises an opticallyanisotropic layer, the optically anisotropic layer including a layercontaining a discotic liquid crystal compound.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention will appear more fully upon considerationof the exemplary embodiments of the invention, which are schematicallyset forth in the drawings, in which:

FIG. 1 is a schematic view showing an example of a liquid crystaldisplay of the background art;

FIG. 2 is a schematic view showing an example of a liquid crystaldisplay of the background art;

FIG. 3 is a schematic view showing an example of a liquid crystaldisplay of the background art;

FIG. 4 is a schematic view of a Poincare sphere, used for explaining achange in a polarized state of an incident light in a liquid crystaldisplay of the background art;

FIG. 5 is a schematic view showing an example of a liquid crystaldisplay of the present invention;

FIG. 6 is a schematic view of a Poincare sphere, used for explaining achange in a polarized state of an incident light in a liquid crystaldisplay of the present invention;

FIG. 7 is a graph showing optical characteristics in an example of anoptical film employed in the present invention;

FIG. 8 is a schematic view of a Poincare sphere, used for explaining apolarized state;

FIG. 9 is a graph showing an example of a relationship between an acylsubstitution degree of cellulose acylate and Rth of an optical film;

FIG. 10 is a graph showing an example of a relationship between aconcentration of an Rth reducing agent and Rth of an optical film;

FIG. 11 is a graph showing an example of a relationship between aconcentration of a wavelength-dependent dispersion regulating agent andΔRth;

FIG. 12 is a schematic view of a Poincare sphere, used for explaining achange in a polarized state in an incident light in a liquid crystaldisplay of the present invention (IPS-1 in Example 11); and

FIG. 13 is a schematic view of a Poincare sphere, used for explaining achange in a polarized state in an incident light in a liquid crystaldisplay of the present invention (IPS-2 in Example 11).

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Although the invention will be described below with reference to theexemplary embodiments thereof, the following exemplary embodiments andmodifications do not restrict the invention.

An exemplary embodiment of the invention allows, through suitableselection of materials and producing process, to independently control awavelength-dependent dispersion of an in-plane retardation and aretardation in a thickness direction of the optical compensation filmand to determine optically optimum values, thereby enabling a view anglecompensation, at all the wavelengths, in a black display state of theliquid display cell. More specifically, as to the raw materials,selections are made on a polymer raw material, and on a type and anamount of an additive for controlling optical characteristics. As aresult, a liquid crystal display of an exemplary embodiment of thepresent invention is improved in a light leakage in an inclineddirection in a black display state, with a significant improvement in acontrast over a wide viewing angle. Also the liquid crystal display,being capable of suppressing a light leakage in an inclined direction ina black display state over the entire visible wavelength region, issignificantly improved on a color aberration on the black display state,which is dependent on the viewing angle and which has been a drawback inthe prior technology.

In the following, an exemplary embodiment of the present invention willbe explained with reference to accompanying drawings. One aspect of thepresent invention is effective in all the liquid crystal modes,regardless of the driving system of the liquid crystal display, but FIG.1 shows, as an example, a schematic view illustrating a structure of aliquid crystal display of an ordinary VA mode. The liquid crystaldisplay of VA mode includes a liquid crystal cell 3 containing a liquidcrystal layer, in which liquid crystals are aligned perpendicularly to asubstrate surface in the absence of a voltage application, namely in ablack display state, and polarizing plates 1, 2 so positioned that theliquid crystal cell 3 is sandwiched therebetween and that directions oftransmission axes thereof (indicated by stripes in FIG. 1) areperpendicular each other. In FIG. 1, a light is assumed to enter fromthe side of the polarizing plate 1. When a light enters along z-axis inthe absence of a voltage application, the light transmitted by thepolarizing plate 1 is transmitted by the liquid crystal cell 3 whilemaintaining a linearly polarized state, and is completely intercepted bythe polarizing plate 2. As a result, a high contrast image can bedisplayed.

However, the situation becomes different in case of an inclined incidentlight, as shown in FIG. 2. When a light enters from an inclineddirection different from the direction of z-axis and inclined withrespect to the polarizing directions of the polarizing plates 1, 2(so-called off-axis direction), the incident light is influenced, uponpassing through the vertically aligned liquid crystal layer of theliquid crystal cell 3, by a retardation in an inclined direction therebycausing a change in the polarization state. Also the apparenttransmission axes of the polarizing plates 1 and 2 are displaced from anorthogonal relationship. Because of these two factors, the incidentlight from an inclined off-axis direction is not completely interceptedby the polarizing plate 2 to induce a light leakage in a black displaystate, thereby reducing the contrast.

Now a polar angle and an azimuthal angle are defined as follows. Thepolar angle means an inclination angle from a normal direction to thefilm surface, namely from z-axis in FIGS. 1 and 2, and, for example, anormal direction to the film surface is a direction with a polarangle=0°. The azimuthal angle means a direction measuredcounterclockwise from a positive x-axis, and, for example, the positivedirection of x-axis has an azimuthal angle=0°, and the positivedirection of y-axis has an azimuthal angle=90°. The inclined off-axisdirection mentioned above means a case where the polar angle isnon-zero, and principally indicates a case where the azimuthal angle is45, 135, 225 or 315°.

FIG. 3 is a schematic view showing a structure for explaining thefunction of a polarized light in an ordinary liquid crystal display. Thestructure shown in FIG. 3 includes, in addition to the structure shownin FIG. 1, an optical compensation film 4 between the liquid crystalcell 3 and the polarizing plate 1. In the VA-mode liquid crystal displayof such structure, the optical compensation film 4 generally has, at awavelength of 550 nm, Re(550) of from about 20 to 100 nm and Rth(550) offrom about 100 to 300 nm. Also when the optical compensation film 4 isprepared from a material having a positive refractive index anisotropy,it generally meets conditions of Re(450)≧Re(550)≧Re(650) andRth(450)≧Rth(550)≧Rth(650), thus having Re and Rth larger at a shorterwavelength.

FIG. 4 explains the compensation mechanism shown in FIG. 3, by aPoincare sphere. The Poincare sphere is a three-dimensional mapdescribing a polarization state, wherein a position on an equator of thesphere indicates a linearly polarized light. The light propagates in adirection with an azimuthal angle of 45° and a polar angle of 34°. InFIG. 4, an S2-axis perpendicularly penetrates the plane of drawing fromabove to below, and FIG. 4 shows a view of the Poincare sphere from thepositive side of the S2-axis. In FIG. 4 which is a planarrepresentation, a displacement between points before and after a changein the polarization state is represented by a linear arrow showntherein, but a change in the polarization state by passing through theliquid crystal layer or the optical compensation film is represented, onthe actual Poincare sphere, by a rotation by a specified angle about aspecified axis determined according to the optical characteristics.

A polarization state of the incident light, after passing the polarizingplate 1 in FIG. 3, corresponds to a point (i) in FIG. 4, and apolarization state to be intercepted by the absorption axis of thepolarizing plate 2 in FIG. 3 corresponds to a point (ii) in FIG. 4. Inthe prior VA-mode liquid crystal display, a light leakage in theinclined off-axis direction results from a fact that the points (i) and(ii) are displaced each other. The optical compensation film isgenerally used for changing the polarization state of the incident lightfrom the point (i) to the point (ii), including a change in thepolarization state in the liquid crystal layer. Since the liquid crystallayer of the liquid crystal cell 3 shows a positive refractive indexanisotropy and has a vertical alignment, a change in the polarizationstate of the incident light, caused by passing the liquid crystal layer,is represented, on the Poincare sphere, by a downward arrow in FIG. 4 ora rotation about an S1-axis.

A rotation angle about the S1-axis is proportional to a value Δn′d′/λ,obtained by dividing an effective retardation Δn′d′ in an inclineddirection of the liquid crystal layer with the wavelength λ of thelight, so that the rotation angle becomes different among the differentwavelengths of R, G and B. Therefore, after the rotation, a light ofeither of the wavelengths R, G and B becomes displaced from the point(ii). The light of such displaced wavelength is not intercepted by thepolarizing plate 2, thereby causing a light leakage. Since a color ofthe light is defined by a sum of R, G and B, a light leakage of aspecified wavelength results in a change in the proportion, in the sumof R, G and B, thereby causing a color shift. This phenomenon isobserved as a “color shift” when a liquid crystal display is observedfrom an inclined direction.

In the present specification, the lights of R, G and B are representedrespectively by wavelengths of 650 nm for R, 550 nm for G and 450 nm forB. These wavelengths may not necessarily represent the lights or R, Gand B, but are considered suitable for defining optical characteristicsproviding the effects of the present invention.

As explained above, when the optical compensation film 4 is preparedfrom a material having a positive refractive index anisotropy, itgenerally meet conditions of Re(450)≧Re(550)≧Re(650) andRth(450)≧Rth(550)≧Rth(650), thus having Re and Rth larger at a shorterwavelength, so that, when the liquid crystal display is observed from aninclined direction, the effective retardation becomes larger for ashorter wavelength (R≦G≦B). As the displacement amount from the point(i) is dependent on the magnitude of such effective retardation, thedisplacement amounts become R≦G≦B so that the three points do not matchmutually.

Also as to the change in the polarization state of the light uponpassing through the liquid crystal cell, since the liquid crystalmolecules of the liquid crystal cell generally have a positive intrinsicbirefringence and have Re and Rth larger in a shorter wavelength, theeffective retardation when the liquid crystal display is observed froman inclined direction becomes larger for a shorter wavelength. Thereforethe displacement to the point (ii) becomes larger for a shorterwavelength and the lights of R, G and B assume a positional relationshipas shown in FIG. 4.

According to one aspect of the present invention, therefore, an opticalfilm 5 is employed for matching the positions of R, G and B at the point(ii). FIG. 5 is a schematic view showing an example of structure, forexplaining a function of the present invention. The optical film 5 ofthe invention is positioned between the liquid crystal cell 3 and thepolarizing plate 2, but such position is not particularly restricted inthe present invention.

FIG. 6 is a view explaining a compensation mechanism in the structureshown in FIG. 5, utilizing a Poincare sphere. Insertion of an opticalfilm 5 allows to match the lights of R, G and B at a substantially samepoint. More specifically, optical compensations are made on the lightsof wavelengths R, G and B, entering in an inclined direction, with aphase retarding axis and a retardation respectively different for eachwavelength. More specifically, among R, G and B, a wavelength R (650 nm)is in a position at upper right to the point (ii), and a left-downwarddisplacement to the point (ii) requires a positive Re(650) and anegative Rth(650) in the optical film 5. Similarly, as a wavelength G(550 nm) need not be displaced from the point (ii), Re(550) and Rth(550)may both be zero. Also a wavelength B (450 nm) is in a position at lowerleft to the point (ii), and a right-upward displacement to the point(ii) requires a negative Re(450) and a positive Rth(450) in the opticalfilm 5. In the optical film 5 having such optical characteristics, thewavelength dependences of Re and Rth are shown in FIG. 7.

The foregoing discussion is applicable, in the optical compensation inan ordinary liquid crystal display, to all the cases where a centralwavelength G (550 nm) is matched with the point (ii) but wavelengths Rand B are not matched with this point. FIG. 8 is a magnified view of aperipheral area around the point (ii) on the Poincare sphere, withpoints 1-9 displaced from the point (ii), and Table 1 shows theproperties required for the optical film 5 for displacing these points1-9 to the point (ii). In FIG. 8 and Table 1, a point 5 is same as thepoint (ii).

TABLE 1 position Re Rth 1 negative negative 2 0 negative 3 positivenegative 4 negative 0 5 0 0 6 positive 0 7 negative positive 8 0positive 9 positive positive

The cases where, among the wavelengths R, G and B, the wavelength G (550nm) is matched with the target point 5 but wavelengths R and B cannot bematched with the point 5, can be divided into cases (1) to (8) in Table2, utilizing the points 1 to 9 in FIG. 8, and these cases can beclassified into four classes A=(1) and (2), B=(3) and (4), C=(5) and (6)and D=(7) and (8) (cf. Table 2). The Re and Rth values required for theoptical film 5 are obtained from Table 1, and the wavelength dependencesof Re and Rth are summarized in Table 3.

TABLE 2 Position class case B (450 nm) G (550 nm) R (650 nm) A (1) 2 5 8(2) 1 5 9 B (3) 4 5 6 (4) 7 5 3 C (5) 8 5 2 (6) 9 5 1 D (7) 6 5 4 (8) 35 7 Ideal 5 5 5

In the foregoing description, there is shown a case where, among thewavelengths R, G and B, the central wavelength G (550 nm) becomes anideal point (ii), where both Re(550) and Rth(550) are zero, but, in anactual liquid crystal display, it may be difficult to realize asituation where both Re(550) and Rth(550) are completely zero. Though itis desirable that Re(550) and Rth(550) are both zero as far as possible,the present inventors find, as a range where Re(550) and Rth(550) areclose to zero and color shifts are tolerable, that the optical film ofthe invention should have optical performances of 0≦Re(550)≦10 nm and−25≦Rth(550)≦25 (nm), preferably 0≦Re(550)≦5 nm and −15≦Rth(550)≦15(nm).

Thus, according to one aspect of the present invention, the wavelengthsR, G and B, which are separated in front of the polarizing plate at theexit side of the liquid crystal display, may be made to coincide therebyavoiding the light leakage, by utilizing an optical film of a wavelengthdependence selected among A, B, C and D classified in Table 3.Therefore, in any liquid crystal mode or in the structure with anyoptical material or any optical components, the optical film of theinvention allows to prevent a color shift in an observation from aninclined direction, by wavelength dependences of Re and Rth selectedamong A, B, C and D classified in Table 3. Thus the scope of the presentinvention is not restricted by the display mode of the liquid crystallayer but is applicable to the liquid crystal display with the liquidcrystal layer of any display mode, such as a VA mode, an IPS mode, anOCB mode, a TN mode or an ECB mode.

An optical film of the present invention is characterized in that aretardation thereof satisfies relations (1) to (3):

0≦Re(550)≦10;  (1)

−25≦Rth(550)≦25; and  (2)

|I|+|II|+|III|+|IV|>0.5 (nm),  (3)

wherein:

I=Re(450)-Re(550);

II=Re(650)-Re(550);

III=Rth(450)-Rth(550); and

IV=Rth(650)-Rth(550).

The relations (1) and (2) indicate, as described above, that Re(550) andRth(550) have to be as close to zero as possible in the optical film ofthe invention. The relation (3) indicates that appropriate wavelengthdependences are necessary for Re and Rth, in order to match R, G and Bon the liquid crystal display. A film of an optical performance notsatisfying the relation (3) has scarce wavelength dependences for Re andRth, and is incapable of reducing the color shift found when the liquidcrystal display is observed from an inclined direction.

The relation (3) is preferably

|I|+|II|+|III|+|IV|>2.0 (nm),

more preferably

|I|+|II|+|III|+|IV|>4.0 (nm).

The optical film of the invention can be classified into A, B, C and Das described above, which respectively have following opticalperformances.

Among the optical films of the invention, an optical film belonging tothe class A meets the relations (1) to (3) above and preferablysatisfies following relations (4-A) to (7-A):

−50≦I≦0;  (4-A)

0≦II≦50;  (5-A)

−50≦III≦0; and  (6-A)

0<IV≦50,  (7-A)

and more preferably:

−25≦I≦0;  (4-A′)

0≦II≦25;  (5-A′)

−25≦III<0; and  (6-A′)

0<IV≦25.  (7-A′)

Among the optical films of the invention, an optical film belonging tothe class B meets the relations (1) to (3) above and preferablysatisfies following relations (4-B) to (7-B):

−50≦I<0;  (4-B)

0<II≦50;  (5-B)

0≦III≦50; and  (6-B)

−50≦IV≦0,  (7-B)

and more preferably:

−25≦I<0;  (4-B′)

0<II≦25;  (5-B′)

0≦III≦25; and  (6-B′)

−25≦IV≦0.  (7-B′)

Among the optical films of the invention, an optical film belonging tothe class C meets the relations (1) to (3) above and preferablysatisfies following relations (4-C) to (7-C):

0≦I≦50;  (4-C)

−50≦II≦0;  (5-C)

0<III≦50; and  (6-C)

−50≦IV<0,  (7-C)

and more preferably:

0≦I≦25;  (4-C′)

−25≦II≦0;  (5-C′)

0<III≦25; and  (6-C′)

−25≦IV<0.  (7-C′)

Among the optical films of the invention, an optical film belonging tothe class D meets the relations (1) to (3) above and preferablysatisfies following relations (4-D) to (7-D):

0<I≦50;  (4-D)

−50≦II<0;  (5-D)

−50≦III≦0; and  (6-D)

9≦IV≦50,  (7-D)

and more preferably:

10≦I≦50;  (4-D′)

−50≦II≦−10;  (5-D′)

−50≦III≦−30; and  (6-D′)

30≦IV≦50.  (7-D′)

(Retardation and Wavelength-Dependent Dispersion Thereof)

In the present specification, Re(λ) and Rth(λ) respectively indicate anin-plane retardation and a retardation in a thickness direction, at awavelength λ. Re(λ) can be measured, in an instrument KOBRA 21ADH(manufactured by Oji Scientific Instruments Ltd.), by introducing alight of a wavelength of λ nm in a normal direction to the film surface.Rth(λ) can be obtained by measuring Re(λ) at 11 points with a light of awavelength of X nm introduced with inclination angles of from −50° to+50° at a pitch of 10° with respect to the normal direction to the filmsurface, taking an in-plane phase-retarding axis (judged by KOBRA 2lADH) as an inclination axis (rotation axis), and by a calculationexecuted by KOBRA 21ADH based on thus measured retardations, an assumedaverage refractive index and an entered film thickness. In case of anIPS mode, Rth(λ) is obtained by measuring Re(λ) at 6 points with a lightof a wavelength of λ nm introduced with inclination angles of from anormal direction to the film surface to 50° at a pitch of 10° withrespect to the normal direction, taking an in-plane phase-retarding axis(judged by KOBRA 21ADH) as an inclination axis (rotation axis) (in theabsence of a phase-retarding axis, an arbitrary direction in the filmplane being taken as a rotary axis), and by a calculation executed byKOBRA 21ADH based on thus measured retardations, an assumed averagerefractive index and an entered film thickness. It is also possible tomeasure retardations at two arbitrary directions, taking thephase-retarding axis as an inclination axis (rotation axis) (in theabsence of a phase-retarding axis, an arbitrary direction in the filmplane being taken as a rotary axis), and to calculate Rth based on thusmeasured values, an assumed average refractive index and an entered filmthickness, according to following equations (1) and (2). The assumedaverage refractive index may be obtained from Polymer Handbook (JohnWiley & Sons, Inc.) or from catalog values of various optical films. Anaverage refractive index, if not already known, may be obtained by ameasurement with Abbe's refractometer. Examples of the averagerefractive index on principal optical films are as follows: celluloseacylate 1.48, cycloolefin polymer 1.52, polycarbonate 1.59, polymethylmethacrylate 1.49, and polystyrene 1.59. The KOBRA 21ADH calculates nx,ny and nz based on such assumed average refractive index and a filmthickness, and further calculates Nz=(nx−nz)/(nx−ny) based on thuscalculated nx, ny and nz.

$\begin{matrix}{{{Re}(\theta)} = {\left\lbrack {{nx} - \frac{{ny} \times {nz}}{\sqrt{\begin{matrix}{\left\{ {{ny}\mspace{11mu} {\sin \left( {\sin^{- 1}\left( \frac{\sin \left( {- \theta} \right)}{nx} \right)} \right)}} \right\}^{2} +} \\\left\{ {{nz}\mspace{11mu} {\cos \left( {\sin^{- 1}\left( \frac{\sin \left( {- \theta} \right)}{nx} \right)} \right)}} \right\}^{2}\end{matrix}}}} \right\rbrack \times \frac{d}{\cos \left\{ {\sin^{- 1}\left( \frac{\sin \left( {- \theta} \right)}{nx} \right)} \right\}}}} & (1)\end{matrix}$

Note: Re(θ) indicates a retardation in a direction inclined by an angleθ from the normal direction.

Rth=((nx+ny)/2−nz)×d  (2)

In the equations (1) and (2), d indicates a film thickness.

(Material for Optical Film)

A material constituting the optical film of the invention is preferablya polymer satisfactory in optical performance, transparency, mechanicalstrength, thermal stability, moisture shielding property, isotropicproperty and the like, and may be any material having Re and Rth withinthe ranges meeting the aforementioned optical performances. Examples ofsuch polymer include a polycarbonate-type polymer, a polyester polymersuch as polyethylene terephthalate or polyethylene naphthalate, anacrylic polymer such as polymethyl methacrylate, and a styrenic polymersuch as polystyrene or an acrylonitrile-styrene copolymer (AS resin).Examples further include a polyolefin such as polyethylene orpolypropylene, a polyolefnic polymer such as an ethylene-propylenecopolymer, a vinyl chloride-based polymer, an amide-based polymer suchas nylon or an aromatic polyamide, an imide-based polymer, asulfone-based polymer, a polyethersulfone-type polymer, a polyetherether ketone-type polymer, a polyphenylene sulfide-type polymer, avinylidene chloride-based polymer, a vinyl alcohol-based polymer, avinyl butyral-based polymer, an allylate-based polymer, apolyoxymethylene-type polymer, an epoxy polymer, and a polymer mixturethereof.

Also as the material constituting the optical film of the invention, athermoplastic norbornene resin may be employed preferably, such asZeonex or Zeonor manufactured by Nippon Zeon Ltd. or Arton manufacturedby JSR Corp.

Also as the material constituting the optical film of the invention, acellulose-based polymer (hereinafter called cellulose acylate), that hasbeen employed as a transparent protective film for a polarizing plate,may be employed particularly preferably. Representative examples ofcellulose acylate include triacetyl cellulose. In the following,cellulose acylate will be explained in detail.

(Raw Material Cotton for Cellulose Acylate)

Raw material cellulose for the cellulose acylate to be employed in theoptical film of the invention includes cotton linter and wood pulp(broad-leaf pulp or needle-leaf pulp), and cellulose acylate obtainedfrom any raw material cellulose may be usable, eventually as a mixtureof plural kinds. Such raw material cellulose is described in detail, forexample, in Plastic Zahyo Koza (17), cellulose fibers (Marusawa & Uda,Nikkan Kogyo Shimbun, 1970) and in Japan Institute of Invention andInnovation, Journal of Technical Disclosure 2001-1745 (p. 7-8), and anycellulose described therein may be utilized without any particularrestriction for the cellulose acylate film.

(Substitution Degree of Cellulose Acylate)

In the following, cellulose acylate produced from the aforementionedcellulose will be explained. The cellulose acylate is obtained byacylating hydroxyl groups of cellulose, with a substituent that may beany one from an acetyl group containing 2 carbon atoms to a substituentcontaining 22 carbon atoms. Cellulose acylate is not particularlyrestricted in a substitution degree in the hydroxyl groups of cellulose,but a substitution degree can be obtained by measuring and calculating abonding degree of acetic acid and/or a fatty acid containing 3 to 22carbon atoms, substituted on the hydroxyl groups of cellulose. Themeasurement may be executed according to ASTM D-817-91.

In cellulose acylate, the substitution degree in the hydroxyl groups ofcellulose is not particularly restricted as described above, but ispreferably within a range of from 2.50 to 3.00, more preferably from2.56 to 3.00 and further preferably from 2.75 to 3.00. A higher acylsubstitution degree allows to reduce the optical anisotropy of the film.

Among acetic acid and/or a fatty acid containing 3 to 22 carbon atoms,to be substituted on the hydroxyl groups of cellulose, an acyl groupcontaining 2 to 22 carbon atoms may be an aliphatic group or an arylgroup, and may be a single group or a mixture of plural groups. Examplesthereof include an alkyl carbonyl ester, an alkenyl carbonyl ester, anaromatic carbonyl ester or an aromatic alkyl carbonyl ester ofcellulose, each of which may further have a substituent. Preferredexamples of such acyl group include acetyl, propionyl, butanoyl,heptanoyl, hexanoyl, octanoyl, decanoyl, dodecanoyl, tridecanoyl,tetradecanoyl, hexadecanoyl, octadecanoyl, iso-butanoyl, t-butanoyl,cyclohexanecarbonyl, oleoyl, benzoyl, naphthylcarbonyl, and cinnamoyl.Among these, acetyl, propionyl, butanoyl, dodecanoyl, octadecanoyl,t-butanoyl, oleoyl, benzoyl, naphthylcarbonyl, and cinnamoyl arepreferable, and acetyl, propionyl and butanoyl are more preferable.

As a result of intensive investigations undertaken by the presentinventors, it is found that, in the case where the acyl substituents onthe hydroxyl groups of cellulose are substantially at least two kindsselected from an acetyl group, a propionyl group and a butanoyl group,the optical anisotropy of the cellulose acylate film can be reduced whenthe total substitution degree is within a range of from 2.50 to 3.00.The acyl substitution degree is more preferably from 2.60 to 3.00, andfurther preferably from 2.65 to 3.00.

(Polymerization Degree of Cellulose Acylate)

The cellulose acylate advantageously employed in the invention has apolymerization degree, in a viscosity-average polymerization degree, offrom 180 to 700, and, in the case of cellulose acetate, it is morepreferably from 180 to 550, further preferably from 180 to 400 andparticularly preferably from 180 to 350. An excessively highpolymerization degree increases the viscosity of a dope solution ofcellulose acylate, whereby a film preparation by a casting method maybecome difficult. Also an excessively low polymerization degree reducesthe strength of the prepared film. An average polymerization degree canbe measured by a limit viscosity method proposed by Uda et al. (KazuoUda and Hideo Saito, J. of Soc. of Fiber Science and Technology, vol.18, No. 1, p. 105-120, 1962), and described in detail in JP-A-9-95538.The optical film of the invention, prepared from cellulose acylate inwhich acyl substituents are substantially constituted of acetyl groupsonly and which has an average polymerization degree of from 180 to 550,can exhibit particularly satisfactory performances.

In cellulose acylate advantageously employed in the invention, amolecular weight distribution is evaluated by gel permeationchromatography, and preferably has a narrow distribution with a smalldispersion index Mw/Mn (Mw: weight-average molecular weight, Mn:number-average molecular weight), preferably within a range of from 2.0to 4.0, more preferably from 2.0 to 3.5, and most preferably from 2.3 to3.3

Elimination of low-molecular components is effective as it reduces theviscosity than in ordinary cellulose acylate, in spite of an increase inthe average molecular weight (polymerization degree). Cellulose acylatewith reduced low-molecular components may be obtained by removinglow-molecular components from cellulose acylate synthesized by anordinary method. The removal of the low-molecular components may beexecuted by washing cellulose acylate with an appropriate organicsolvent. In case of producing cellulose acylate with reducedlow-molecular components, an amount of sulfuric acid catalyst in theacylation reaction is preferably regulated to 0.5 to 25 parts by weight,with respect to 100 parts by weight of cellulose. The sulfuric acidcatalyst, employed in an amount of the aforementioned range, allows tosynthesize cellulose acylate that is preferable also in the molecularweight distribution (having a uniform molecular weight distribution). Atthe manufacture of cellulose acylate, it has a water content preferablyof 2 wt % or less, more preferably 1 wt % or less, and particularlypreferably 0.7 wt % or less. Cellulose acylate generally contains water,normally about 2.5 to 5 wt %. In order to realize the aforementionedwater content in the invention, a drying is necessary, and it may beexecuted by any method as long as a desired water content is attained.For the cellulose acylate to be employed in the invention, a rawmaterial cotton and a synthesizing method are described in detail inJapan Institute of Invention and Innovation, Journal of TechnicalDisclosure (No. 2001-1745, issued Mar. 15, 2001, JIII), p. 7-12.

Cellulose acylate, having substituents, a substitution degree, apolymerization degree and a molecular weight distribution within theaforementioned ranges, may be employed singly or in a mixture of two ormore different cellulose acylates.

(Additives to Optical Film)

In a solution for preparing the optical film of the invention, variousadditives (such as a compound for reducing optical anisotropy, acompound for increasing optical anisotropy, an agent for regulatingwavelength-dependent dispersion, an ultraviolet absorber, a plasticizer,an anti-aging agent, fine particles and an optical characteristicsregulating agent) may be added according to the purpose in eachpreparation step, and such additives will be explained below. Also suchaddition may be executed at any timing within a dope preparing process,or in an additive-adding step, to be added after a final adjustment stepin the dope preparation process.

(Compound for Reducing Rth)

The optical film of the invention preferably contains at least acompound capable of reducing a retardation Rth(550) in the thicknessdirection of the film (such compound being hereinafter referred to asRth reducing agent), within a range capable of meeting relations (8) and(9):

(Rth(A)−Rth(0))/A≦−1.0; and  (8)

0.01≦A≦30.  (9)

The relations (8) and (9) are more preferably represented as:

(Rth(A)−Rth(0))/A≦−2.0; and  (8′)

0.01≦A≦20,  (9′)

and further preferably represented as:

(Rth(A)−Rth(0))/A≦−3.0; and  (8″)

0.01≦A≦15,  (9″)

wherein:

Rth(A) means Rth(nm) at 550 nm of an optical film containing thecompound capable of reducing Rth(550) by A %;

Rth(0) means Rth(nm) at 550 nm of an optical film not containing thecompound capable of reducing Rth(550); and

A means a weight (%) of the compound capable of reducing Rth(550) withrespect to the weight (taken as 100) of the raw material polymer of theoptical film.

(Structural Characteristics of Rth Reducing Agent)

A structure and a function of the Rth reducing agent, in the opticalfilm of the invention, will be explained below. In order to sufficientlyreduce the optical anisotropy and to bring both Re and Rth close tozero, it is preferable to utilize a compound capable of suppressing thehigh-molecular polymer in the optical film from being aligned in thein-plane direction and in the thickness direction. Also the compound forreducing optical anisotropy is preferably sufficiently soluble mutuallywith the high-molecular polymer and is preferably free from a rod-shapedstructure or a planar structure in the compound itself. Morespecifically, when the compound has plural planar functional groups suchas aromatic groups, such functional groups preferably are not positionedon a common plane but are provided in a non-planar structure.

The Rth reducing agent may or may not include an aromatic group. Alsothe Rth reducing agent has a molecular weight preferably within a rangeof from 150 to 3,000, more preferably from 170 to 2,000, andparticularly preferably from 200 to 1,000. Within such molecular weightrange, it may have a specified monomer structure, or an oligomerstructure or a polymer structure in which a plurality of such monomerunits are bonded.

(logP Value)

In the preparation of an optical film of the invention, in case ofemploying a hydrophilic polymer such as cellulose acylate as a rawmaterial, it is preferable to utilize, as the Rth reducing agent forsuppressing the high-molecular polymer in the film from being aligned inthe in-plane direction and in the thickness direction, a compound havingan octanol-water distribution coefficient (logP value) within a range offrom 0 to 7. A compound having a logP value of 7 or less shows anexcellent mutual solubility with the high-molecular polymer, thus notcausing drawbacks such as white turbidity or dusty surface in the film.Also a compound having a logP value of 0 or more does not becomeexcessively hydrophilic, thus not causing a drawback such as adeteriorated water resistance of the cellulose acetate film. The logPvalue is more preferably within a range of from 1 to 6, and particularlypreferably from 1.5 to 5.

The octanol-water distribution coefficient (logP value) can be measuredby a flask shaking method described in JIS Z-7260-107(2000). Also theoctanol-water distribution coefficient (logP value) may be estimated,instead of an actual measurement, by a chemical calculational method oran empirical method. The preferred calculational methods includeCrippen's fragmentation method {J. Chem. Inf. Comput. Sci., vol. 27, p.21(1987)}, Viswanadhan's fragmentation method J. Chem. Inf. Comput.Sci., vol. 29, p. 163(1989)}, and Broto's fragmentation method {Eur. J.Med. Chem.—Chim. Theor., vol. 19, p. 71(1984)}, among which Crippen'sfragmentation method is more preferable. When a compound shows differentlogP values by the measuring method and the calculational method,whether such compound is within the scope of the invention is to bejudged by Crippen's fragmentation method.

(Physical Properties of Rth Reducing Agent)

The Rth reducing agent is preferably a liquid at 25° C. or a solidhaving a melting point of from 25 to 250° C., and more preferably aliquid at 25° C. or a solid having a melting point of from 25 to 200° C.Also the Rth reducing agent preferably does not evaporate in the stepsof dope casting and drying in preparing the high-molecular polymer film.

The Rth reducing agent is preferably added in an amount of from 0.01 to30 wt % of the high-molecular polymer, more preferably from 0.05 to 25wt % and particularly preferably from 0.1 to 20 wt %.

The Rth reducing agent may be employed singly or in a mixture of two ormore compounds in an arbitrary ratio. The Rth reducing agent may beadded at any step in the dope preparing process, or at the end of thedope preparing process.

For such Rth reducing agent, compounds disclosed in JP-A-2005-139304 maybe employed advantageously. Among these, preferred is a compoundrepresented by a following formula (1), which will be explained below:

In the formula (1), R¹¹ represents an alkyl group or an aryl group; andR¹² and R¹³ each independently represents a hydrogen atom, an alkylgroup or an aryl group. R¹¹, R¹² and R¹³ particularly preferably contain10 or more carbon atoms in total, and the alkyl group or the aryl groupmay further have a substituent.

The substituent is preferably a fluorine atom, an alkyl group, an acylgroup, an alkoxy group, a sulfone group or a sulfonamide group, andparticularly preferably an alkyl group, an aryl group, an alkoxy group,a sulfone group or a sulfonamide group.

The alkyl group may be linear, branched or cyclic, and preferablycontains 1 to 25 carbon atoms, more preferably 6 to 25 carbon atoms andparticularly preferably 6 to 20 carbon atoms (such as methyl, ethyl,propyl, isopropyl, butyl, isobutyl, t-butyl, amyl, isoamyl, t-amyl,hexyl, cyclohexyl, heptyl, octyl, bicyclooctyl, nonyl, adamantyl, decyl,t-octyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl,heptadecyl, octadecyl, nonadecyl or didecyl).

The aryl group preferably contains 6 to 30 carbon atoms, andparticularly preferably 6 to 24 carbon atoms (such as phenyl, biphenyl,terphenyl, naphthyl, binaphthyl or triphenylphenyl). Preferable examplesof the compound represented by the formula (1) are shown below, but thepresent invention is not limited to such specific examples.

Other examples of the Rth reducing agent include a compound representedby a following formula (2):

In the formula (2), R²¹ represents an alkyl group or an aryl group; andR²² and R²³ each independently represents a hydrogen atom, an alkylgroup or an aryl group. The alkyl group may be linea r, branched orcyclic, and preferably contains 1 to 20 carbon atoms, more preferably 1to 15 carbon atoms and most preferably 1 to 12 carbon atoms. The cyclicalkyl group is particularly preferably a cyclohexyl group. The arylgroup preferably contains 6 to 36 carbon atoms, and more preferably 6 to24 carbon atoms. Also R²¹ and R²² preferably contain 10 or more carbonatoms in total, and the alkyl group or the aryl group may further have asubstituent.

The alkyl group or aryl group may have a substituent, and suchsubstituent is preferably a halogen atom (such as chlorine, bromine,fluorine or iodine), an alkyl group, an aryl group, an alkoxy group, anaryloxy group, an acyl group, an alkoxycarbonyl group, anaryloxycarbonyl group, an acyloxy group, a sulfonylamino group, ahydroxyl group, a cyano group, an amino group or an acylamino group,more preferably a halogen atom, an alkyl group, an aryl group, an alkoxygroup, an aryloxy group, a sulfonylamino group or an acylamino group,and particularly preferably an alkyl group, an aryl group, asulfonylamino group or an acylamino group.

Preferable examples of the compound represented by the formula (2) areshown below, but the present invention is not limited to such specificexamples.

(Wavelength-Dependent Dispersion Regulating Agent)

The optical film of the invention preferably contains, in case ofincreasing the optical anisotropy at the shorter wavelength side, atleast a compound capable of increasing ΔRth and represented by afollowing formula (10) (such compound being hereinafter called awavelength-dependent dispersion regulating agent), within a rangecapable of meeting relations (11) and (12). Though depending on the typeof polymer employed as the raw material for the optical film and on acombination with other additives such as the Rth reducing agent, it ispreferable, in case of increasing Rth at the shorter wavelength side(class B or C in Table 3 above), to increase the amount of thewavelength-dependent dispersion regulating agent with respect to a unitamount of the raw material polymer for the film. On the other hand, incase of decreasing Rth at the shorter wavelength side (class A or D inTable 3 above), it is preferable to decrease the amount of thewavelength-dependent dispersion regulating agent or not to use the same:

ΔRth=Rth(450)−Rth(650);  (10)

(ΔRth(B)−ΔRth(0))/B≧1.0; and  (11)

0.01≦B30.  (12)

The relations (11) and (12) are more preferably represented as:

(ΔRth(B)−ΔRth(0))/B≧5.0; and  (11′)

0.05≦B≦20,  (12′)

and further preferably represented as:

(ΔRth(B)−ΔRth(0))/B≧10.0; and  (11″)

0.1B≦10,  (12″)

wherein:

ΔRth(B) means ΔRth(nm) of an optical film containing the compoundcapable of increasing ΔRth, by B %;

ΔRth(0) means ΔRth(nm) of an optical film not containing the compoundcapable of increasing ΔRth; and

B means a weight (%) of the compound capable of increasing ΔRth withrespect to the weight (taken as 100) of the raw material polymer of theoptical film.

As the wavelength-dependent dispersion regulating agent, it ispreferable to use at least a compound having an absorption within anultraviolet region of from 200 to 400 nm. A compound having anabsorption within an ultraviolet region of from 200 to 400 nm haswavelength-dependent dispersion characteristics showing an absorbancelarger in a shorter wavelength side than in a longer wavelength side.When such compound is isotropically present inside the optical film, thewavelength-dependent dispersion of the birefringence of the compounditself and also of the optical characteristics is estimated to be largerin the shorter wavelength side, as in the wavelength-dependentdispersion of the absorbance.

Therefore, the aforementioned compound, which has an absorption in theultraviolet region of from 200 to 400 nm and which is assumed to have awavelength-dependent dispersion of the optical characteristics of thecompound itself larger at the shorter wavelength side, allows toregulate the wavelength-dependent dispersion of the opticalcharacteristics of the optical film. For this purpose, the compound forregulating the wavelength-dependent dispersion is required to besufficiently soluble mutually with the raw material polymer of the film.In such compound, the absorption range in the ultraviolet region ispreferably from 200 to 400 nm, more preferably from 220 to 395 nm, andfurther preferably from 240 to 390 nm.

In recent liquid crystal displays for use in a television, a notebookpersonal computer or a mobile terminal, optical members to be employedtherein are being required to have a high transmittance in order toobtain a higher luminance with a lower electric power. In considerationof this fact, the wavelength-dependent dispersion regulating agent, tobe added in the optical film, is required to have a satisfactoryspectral transmittance. In the optical film of the invention, itpreferably has a spectral transmittance, at a wavelength of 380 nm, offrom 45 to 95%, and a spectral transmittance, at a wavelength of 350 nm,of 10% or less.

The aforementioned wavelength-dependent dispersion regulating agent,advantageously employed in the invention, preferably has a molecularweight of from 250 to 1,000 in consideration of volatility, morepreferably from 260 to 800, further preferably from 270 to 800, andparticularly preferably from 300 to 800. Within such molecular weightrange, it may have a specified monomer structure, or an oligomerstructure or a polymer structure in which a plurality of such monomerunits are bonded.

The aforementioned wavelength-dependent dispersion regulating agent,advantageously employed in the invention, is preferably employed in anamount of from 0.01 to 30 wt % with respect to the raw material polymerof the film, more preferably from 0.1 to 20 wt % and particularlypreferably from 0.2 to 10 wt %.

(Method of Addition of Wavelength-Dependent Dispersion Regulating Agent)

The wavelength-dependent dispersion regulating agent may be employedsingly or in a mixture of two or more compounds in an arbitrary ratio.The wavelength-dependent dispersion regulating agent may be added at anystep in the dope preparing process, or at the end of the dope preparingprocess.

Specific examples of the wavelength-dependent dispersion regulatingagent, advantageously employed in the invention, include a benzotriazolecompound, a benzophenone compound, a cyano group-containing compound, anoxybenzophenone compound, a salicylate ester compound and a nickelcomplex salt compound, but the present invention is not limited to suchcompounds.

Among the benzotriazole compounds, those represented by a followingformula (3) are preferably employed as the wavelength-dependentdispersion regulating agent of the invention:

Q³¹-Q³²-OH  Formula (3):

wherein Q³¹ represents a nitrogen-containing aromatic heterocycle; andQ³² represents an aromatic ring.

Q³¹ represents a nitrogen-containing aromatic heterocycle, preferably a5- to 7-membered nitrogen-containing aromatic heterocycle, and morepreferably a 5- to 6-membered nitrogen-containing aromatic heterocycle,such as imidazole, pyrrazole, triazole, tetrazole, thiazole, oxazole,selenazole, benzotriazole, benzothiazole, benzoxazole, benzoselenazole,thiadiazole, oxadiazole, naphthothiazole, naphthooxazole,azabenzimidazole, purin, pyridine, pyrazine, pyrimidine, pyridazine,triazine, triazaindene or tetrazaindene, and further preferably a5-membered nitrogen-containing aromatic heterocycle, such as imidazole,pyrrazole, triazole, tetrazole, thiazole, oxazole, benzotriazole,benzothiazole, benzoxazole, thiadiazole, or oxadiazole, and particularlypreferably benzotriazole.

The nitrogen-containing aromatic heterocycle represented by Q³¹ mayfurther have a substituent, to which applicable is a substituent T to beexplained later. Also when plural substituents are present, they may bemutually condensed to further form a ring.

An aromatic ring represented by Q³² may be an aromatic hydrocarbon ringor an aromatic heterocycle. Also it may be a single ring or mayconstitute condensed rings with another ring. The aromatic hydrocarbonring is preferably a single- or two-ringed aromatic hydrocarbon ringcontaining 6 to 30 carbon atoms (such as a benzene ring or a naphthalenering), more preferably an aromatic hydrocarbon ring containing 6 to 20carbon atoms, further preferably an aromatic hydrocarbon ring containing6 to 12 carbon atoms, and most preferably a benzene ring.

The aromatic hetorocycle is preferably an aromatic hetorocyclecontaining a nitrogen atom or a sulfur atom. Specific examples of theheterocycle include thiophene, imidazole, pyrrazole, pyridine, pyrazine,pyridazine, triazole, triazine, indole, indazole, purin, thiazoline,thiazole, thiadiazole, oxazoline, oxazole, oxadiazole, quinoline,isoquinoline, phthalazine, naphthylidine, quinoxaline, quinazoline,cinnoline, pteridine, acridine, phenanthroline, phenazine, tetrazole,benzimidazole, benzoxazole, benzothiazole, benzotriazole andtetrazaindene. The aromatic heterocycle is preferably pyridine, triazineor quinoline.

The aromatic ring represented by Q³² is preferably an aromatichydrocarbon ring, more preferably a naphthalene ring or a benzene ring,and particularly preferably a benzene ring. Q³² may further have asubstituent, preferably a substituent T shown below.

Examples of the substituent T include an alkyl group (preferablycontaining 1 to 20 carbon atoms, more preferably containing 1 to 12carbon atoms and particularly preferably containing 1 to 8 carbon atoms,such as methyl, ethyl, i-propyl, t-butyl, n-octyl, n-decyl, n-hexadecyl,cyclopropyl, cyclopentyl or cyclohexyl), an alkenyl group (preferablycontaining 2-20 carbon atoms, more preferably containing 2 to 12 carbonatoms and particularly preferably containing 2 to 8 carbon atoms, suchas vinyl, allyl, 2-butenyl or 3-pentenyl), an alkinyl group (preferablycontaining 2-20 carbon atoms, more preferably containing 2 to 12 carbonatoms and particularly preferably containing 2 to 8 carbon atoms, suchas propalgyl or 3-pentinyl), an aryl group (preferably containing 6 to30 carbon atoms, more preferably containing 6 to 20 carbon atoms andparticularly preferably containing 6 to 12 carbon atoms, sueh as phenyl,p-methylphenyl or naphthyl), a substituted or non-substituted aminogroup (preferably containing 0 to 20 carbon atoms, more preferablycontaining 0 to 10 carbon atoms and particularly preferably containing 0to 6 carbon atoms, such as amino, methylamino, dimethylamino,diethylamino or dibenzylamino), an alkoxy group (preferably containing1-20 carbon atoms, more preferably containing 1 to 12 carbon atoms andparticularly preferably containing 1 to 8 carbon atoms, such as methoxy,ethoxy, or butoxy), an acyloxy group (preferably containing 6-20 carbonatoms, more preferably containing 6 to 16 carbon atoms and particularlypreferably containing 6 to 12 carbon atoms, such as phenyloxy, or2-naphthyloxy), an acyl group (preferably containing 1 to 20 carbonatoms, more preferably containing 1 to 16 carbon atoms and particularlypreferably containing 1 to 12 carbon atoms, such as acetyl, benzoyl,formyl or pivaloyl), an alkoxycarbonyl group (preferably containing 2 to20 carbon atoms, more preferably containing 2 to 16 carbon atoms andparticularly preferably containing 2 to 12 carbon atoms, such asmethoxycarbonyl or ethoxycarbonyl), an aryloxycarbonyl group (preferablycontaining 7 to 20 carbon atoms, more preferably containing 7 to 16carbon atoms and particularly preferably containing 7 to 10 carbonatoms, such as phenoxycarbonyl), an acyloxy group (preferably containing2 to 20 carbon atoms, more preferably containing 2 to 16 carbon atomsand particularly preferably containing 2 to 10 carbon atoms, such asacetoxy or benzoyloxy), an acylamino group (preferably containing 2 to20 carbon atoms, more preferably containing 2 to 16 carbon atoms andparticularly preferably containing 2 to 10 carbon atoms, such asacetylamino or benzoylamino), an alkoxycarbonylamino group (preferablycontaining 2 to 20 carbon atoms, more preferably containing 2 to 16carbon atoms and particularly preferably containing 2 to 12 carbonatoms, such as methoxycarbonylamino), an aiyloxycarbonylamino group(preferably containing 7 to 20 carbon atoms, more preferably containing7 to 16 carbon atoms and particularly preferably containing 7 to 12carbon atoms, such as phenyloxycarbonylamino), a sulfonylamino group(preferably containing 1 to 20 carbon atoms, more preferably containing1 to 16 carbon atoms and particularly preferably containing 1 to 12carbon atoms, such as methanesulfonylamino or benzenesulfonylamino), asulfamoyl group (preferably containing 0 to 20 carbon atoms, morepreferably containing 0 to 16 carbon atoms and particularly preferablycontaining 0 to 12 carbon atoms, such as sulfamoyl, methylsulfamoyl,dimethylsulfamoyl or phenylsulfamoyl), a carbamoyl group (preferablycontaining 1 to 20 carbon atoms, more preferably containing 1 to 16carbon atoms and particularly preferably containing 1 to 12 carbonatoms, such as carbamoyl, methylcarbamoyl, diethylcarbamoyl orphenylcarbamoyl), an alkylthio group (preferably containing 1 to 20carbon atoms, more preferably containing 1 to 16 carbon atoms andparticularly preferably containing 1 to 12 carbon atoms, such asmethylthio, or ethylthio), an arylthio group (preferably containing 6 to20 carbon atoms, more preferably containing 6 to 16 carbon atoms andparticularly preferably containing 6 to 12 carbon atoms, such asphenylthio), a sulfonyl group (preferably containing 1 to 20 carbonatoms, more preferably containing 1 to 16 carbon atoms and particularlypreferably containing 1 to 12 carbon atoms, such as mesyl or tosyl), asulfinyl group (preferably containing 1 to 20 carbon atoms, morepreferably containing 1 to 16 carbon atoms and particularly preferablycontaining 1 to 12 carbon atoms, such as methanesulfinyl orbenzenesulfinyl), an ureido group (preferably containing 1 to 20 carbonatoms, more preferably containing 1 to 16 carbon atoms and particularlypreferably containing 1 to 12 carbon atoms, such as ureido, methylureidoor phenylureido), a phosphoric acid amide group (preferably containing 1to 20 carbon atoms, more preferably containing 1 to 16 carbon atoms andparticularly preferably containing 1 to 12 carbon atoms, such asdiethylphosphoric acid amide or phenylphosphoric acid amide), a hydroxylgroup, a mercapto group, a halogen atom (such as a fluorine atom, achlorine atom, a bromine atom or an iodine atom), a cyano group, a sulfogroup, a carboxyl group, a nitro group, a hydroxamic acid group, asulfino group, a hydrazino group, an imino group, a heterocyclic group(preferably containing 1 to 30 carbon atoms, and more preferablycontaining 1 to 12 carbon atoms, and including a nitrogen atom, anoxygen atom, or a sulfur atom as a hetero atom, such as imidazolyl,pyridyl, quinolyl, fu yl, piperidyl, morpholino, benzoxazolyl,benzimidazolyl or benzothiazolyl), and a silyl group (preferablycontaining 3 to 40 carbon atoms, more preferably containing 3 to 30carbon atoms and particularly preferably containing 3 to 24 carbonatoms, such as trimethylsilyl or triphenylsilyl). These substituents maybe further substituted. Also when two or more substituents are present,they may be mutually same or different. Also they may be mutuallyconnected to form a ring, if possible.

The compound of the formula (3) is preferably represented by a followingformula (3-1).

In the formula (3-1), R³¹, R³², R³³, R³⁴, R³⁵, R³⁶, R³⁷ and R³⁸ eachindependently represent a hydrogen atom or a substituent, to which theaforementioned substituent T is applicable. Also such substituent may befurther substituted with another substituent, and substituents may bemutually condensed to form a ring structure.

R³¹ and R³³ each is preferably a hydrogen atom, an alkyl group, analkenyl group, an alkinyl group, an aryl group, a substituted ornon-substituted amino group, an alkoxy group, an aryloxy group, ahydroxyl group, or a halogen atom, more preferably a hydrogen atom, analkyl group, an aryl group, an alkyloxy group, an aryloxy group, or ahalogen atom, further preferably a hydrogen atom or an alkyl groupcontaining 1 to 12 carbon atoms, and particularly preferably an alkylgroup containing 1 to 12 carbon atoms (preferably containing 4 to 12carbon atoms).

R³² and R³⁴ each is preferably a hydrogen atom, an alkyl group, analkenyl group, an alkinyl group, an aryl group, a substituted ornon-substituted amino group, an alkoxy group, an aryloxy group, ahydroxyl group, or a halogen atom, more preferably a hydrogen atom, analkyl group, an aryl group, an alkyloxy group, an aryloxy group, or ahalogen atom, further preferably a hydrogen atom or an alkyl groupcontaining 1 to 12 carbon atoms, and particularly preferably a hydrogenatom or a methyl group, and most preferably a hydrogen atom.

R³⁵ and R³⁸ each is preferably a hydrogen atom, an alkyl group, analkenyl group, an alkinyl group, an aryl group, a substituted ornon-substituted amino group, an alkoxy group, an aryloxy group, ahydroxyl group, or a halogen atom, more preferably a hydrogen atom, analkyl group, an aryl group, an alkyloxy group, an aryloxy group, or ahalogen atom, further preferably a hydrogen atom or an alkyl groupcontaining 1 to 12 carbon atoms, and particularly preferably a hydrogenatom or a methyl group, and most preferably a hydrogen atom.

R³⁶ and R³⁷ each is preferably a hydrogen atom, an alkyl group, analkenyl group, an alkinyl group, an aryl group, a substituted ornon-substituted amino group, an alkoxy group, an aryloxy group, ahydroxyl group, or a halogen atom, more preferably a hydrogen atom, analkyl group, an aryl group, an alkyloxy group, an aryloxy group, or ahalogen atom, further preferably a hydrogen atom or a halogen atom, andparticularly preferably a hydrogen atom or a chlorine atom.

The compound of the formula (3) is more preferably represented by afollowing formula (3-2).

In the formula, R³¹, R³³, R³⁶ and R³⁷ have same meaning and samepreferable range as those in the formula (3-1).

Specific examples of the compound represented by the formula (3) areshown below, but the present invention is not at all restricted to suchexamples.

Among the triazole compounds cited above as examples, those having amolecular weight of 320 or higher are advantageous in the storageproperty and preferable for the preparation of the optical film of theinvention

Also the benzophenone compound, which is one of the wavelength-dependentdispersion regulating agents to be employed in the invention, ispreferably that represented by a formula (4).

In the formula, Q⁴¹ and Q⁴² each independently represents an aromaticring; and X⁴¹ represents NR⁴¹ (R⁴¹ representing a hydrogen atom or asubstituent), an oxygen atom or a sulfur atom.

The aromatic ring represented by Q⁴¹ and _(Q)42 may be an aromatichydrocarbon ring or an aromatic heterocycle. These may be a single ring,or may form a condensed ring with another ring.

The aromatic hydrocarbon ring represented by Q⁴¹ and Q⁴² is M preferablya onocyclic or bicyclic aromatic hydrocarbon ring containing 6 to 30carbon atoms (such as a benzene ring or a naphthalene ring), morepreferably an aromatic hydrocarbon ring containing 6 to 20 carbon atoms,further preferably an aromatic hydrocarbon ring containing 6 to 12carbon atoms, and still preferably a benzene ring.

The aromatic heterocycle represented by Q⁴¹ and Q⁴² is preferably anaromatic heterocycle containing at least one of either one of an oxygenatom, a nitrogen atom and a sulfur atom. Specific examples of theheterocycle include furan, pyrrole, thiophene, imidazole, pyrazole,pyridine, pyrazine, pyridazine, triazole, triazine, indole, indazole,purin, thiazoline, thiazole, thiadiazole, oxazoline, oxazole,oxadiazole, quinoline, isoquinoline, phthalazine, naphthyridine,quinoxaline, quinazoline, cinnoline, pteridine, acridine,phenanthroline, phenazine, tetrazole, benzimidazole, benzoxazole,benzothiazole, benzotriazole, and tetrazaindene. The aromaticheterocycle is preferably pyridine, triazine or quinoline.

The aromatic ring represented by Q⁴¹ and Q⁴² is preferably an aromatichydrocarbon ring, more preferably an aromatic hydrocarbon ringcontaining 6 to 10 carbon atoms, and further preferably a substituted ornon-substituted benzene ring.

Q⁴¹ and Q⁴² may further have a substituent, which is preferably theaforementioned substituent T, but the substituent does not include acarboxylic acid, a sulfonic acid or a quaternary ammonium salt. Alsowhen possible, substituents may be linked each other to form a cyclicstructure.

X⁴¹ represents NR42 (R⁴² representing a hydrogen atom or a substituent,to which the aforementioned substituent T may be applicable), an oxygenatom or a sulfur atom, and X⁴¹ is preferably NR⁴² (R⁴² being preferablyan acyl group, or a sulfonyl group, and such substituent may be furthersubstituted), or oxygen, and particularly preferably oxygen.

The compounds represented by the formula (4) are preferably thoserepresented by a following formula (4-1).

In the formula, R⁴¹¹, R⁴¹², R⁴¹³, R⁴¹⁴, R⁴¹⁵, R⁴¹⁶, R⁴¹⁷, R⁴¹⁸ and R⁴¹⁹each independently represents a hydrogen atom or a substituent, to whichthe aforementioned substituent T is applicable. Also these substituentsmay be further substituted with another substituent, or may be mutuallycondensed to form a cyclic structure.

R⁴¹¹, R⁴¹³, R⁴¹⁴, R⁴¹⁵, R⁴¹⁶, R⁴¹⁸ and R⁴¹⁹ each is preferably ahydrogen atom, an alkyl group, an alkenyl group, an alkinyl group, anaryl group, a substituted or non-substituted amino group, an alkoxygroup, an aryloxy group, a hydroxyl group, or a halogen atom, morepreferably a hydrogen atom, an alkyl group, an aryl group, an alkyloxygroup, an aryloxy group, or a halogen atom, further preferably ahydrogen atom or an alkyl group containing 1 to 12 carbon atoms,particularly preferably a hydrogen atom or a methyl group, and mostpreferably a hydrogen atom.

R⁴¹² ispreferably a hydrogen atom, an alkyl group, an alkenyl group, analkinyl group, an aryl group, a substituted or non-substituted aminogroup, an alkoxy group, an aryloxy group, a hydroxyl group, or a halogenatom, more preferably a hydrogen atom, an alkyl group containing 1 to 20carbon atoms, an amino group containing 0 to 20 carbon atoms, an alkoxygroup containing 1 to 12 carbon atoms, an aryloxy group containing 6 to12 carbon atoms, or a hydroxyl group, further preferably an alkoxy groupcontaining 1 to 20 carbon atoms, and particularly preferably an alkoxygroup containing 1 to 12 carbon atoms.

R⁴¹⁷ is preferably a hydrogen atom, an alkyl group, an alkenyl group, analkinyl group, an aryl group, a substituted or non-substituted aminogroup, an alkoxy group, an aryloxy group, a hydroxyl group, or a halogenatom, more preferably a hydrogen atom, an alkyl group containing 1 to 20carbon atoms, an amino group containing 0 to 20 carbon atoms, an alkoxygroup containing 1 to 12 carbon atoms, an aryloxy group containing 6 to12 carbon atoms, or a hydroxyl group, further preferably a hydrogenatom, or an alkyl group containing 1 to 20 carbon atoms (preferablycontaining 1 to 12 carbon atoms, more preferably containing 1 to 8carbon atoms and further preferably a methyl group), and particularlypreferably a methyl group or a hydrogen atom.

The compounds represented by the formula (4) are more preferably thoserepresented by a following formula (4-2).

In the formula, R⁴²⁰ represents a hydrogen atom, a substituted ornon-substituted alkyl group, a substituted or non-substituted alkenylgroup, a substituted or non-substituted alkinyl group, or a substitutedor non-substituted aryl group, and the aforementioned substituent T isapplicable as the substituent. R⁴²⁰ is preferably a substituted ornon-substituted alkyl group, more preferably a substituted ornon-substituted alkyl group containing 5 to 20 carbon atoms, furtherpreferably a substituted or non-substituted alkyl group containing 5 to12 carbon atoms (such as an n-hexyl group, a 2-ethylhexyl group, ann-octyl group, an n-decyl group, an n-dodecyl group, or a benzyl group),and particularly preferably a substituted or non-substituted alkyl groupcontaining 6 to 12 carbon atoms (such as a 2-ethylhexyl group, ann-octyl group, an n-decyl group, an n-dodecyl group or a benzyl group).

The compounds represented by the formula (4) may be synthesized by aknown method, described in JP-A-11-12219.

Specific examples of the compound represented by the formula (4) areshown below, but the present invention is not limited to those specificexamples.

Also the compound containing a cyano group, which is one of thewavelength-dependent dispersion regulating agents to be employed in theinvention, is preferably that represented by a formula (5).

In the formula, Q⁵¹ and Q⁵² each independently represents an aromaticring; and X⁵¹ and X⁵² each represents a hydrogen atom or a substituentand at least either represents a cyano group, a carbonyl group, asulfonyl group or an aromatic heterocycle. The aromatic ring representedby Q⁵¹ and Q⁵² may be an aromatic hydrocarbon ring or an aromaticheterocycle. These may be a single ring, or may form a condensed ringwith another ring.

The aromatic hydrocarbon ring is preferably a monocyclic or bicyclicaromatic hydrocarbon ring containing 6 to 30 carbon atoms (such as abenzene ring or a naphthalene ring), more preferably an aromatichydrocarbon ring containing 6 to 20 carbon atoms, further preferably anaromatic hydrocarbon ring containing 6 to 12 carbon atoms, and stillpreferably a benzene ring.

The aromatic heterocycle is preferably an aromatic heterocyclecontaining a nitrogen atom or a sulfur atom. Specific examples of theheterocycle include thiophene, imidazole, pyrazole, pyridine, pyrazine,pyridazine, triazole, triazine, indole, indazole, purin, thiazoline,thiazole, thiadiazole, oxazoline, oxazole, oxadiazole, quinoline,isoquinoline, phthalazine, naphthyridine, quinoxaline, quinazoline,cinnoline, pteridine, acridine, phenanthroline, phenazine, tetrazole,benzimidazole, benzoxazole, benzothiazole, benzotriazole, andtetrazaindene. The aromatic heterocycle is preferably pyridine, triazineor quinoline.

The aromatic ring represented by Q⁵¹ and Q⁵² is preferably an aromatichydrocarbon ring, and more preferably a benzene ring. Q⁵¹ and Q⁵² mayfurther have a substituent, which is preferably the aforementionedsubstituent T.

X⁵¹ and X⁵² represents a hydrogen atom or a substituent, and at leasteither one is a cyano group, a carbonyl group, a sulfonyl group, or anaromatic heterocycle. The aforementioned substituent T may be applicableto the substituent represented by X⁵¹ and X⁵². Also the substituentrepresented by X^(m) and X⁵² may be further substituted with anothersubstituent, and X⁵¹ and X⁵² may be mutually condensed to form a cyclicstructure.

X⁵¹ and X⁵² each is preferably a hydrogen atom, an alkyl group, an acylgroup, a cyano group, a nitro group, a carbonyl group, a sulfonyl groupor an aromatic heterocycle, more preferably a cyano group, a carbonylgroup, a sulfonyl group or an aromatic heterocycle, further preferably acyano group or a carbonyl group, and particularly preferably a cyanogroup or an alkoxycarbonyl group {—C(═O)}OR⁵¹ (R⁵¹ being an alkyl groupcontaining 1 to 20 carbon atoms, an aryl group containing 6 to 12 carbonatoms or a combination thereof)}.

The compounds represented by the formula (5) are preferably thoserepresented by a following formula (5-1).

In the formula, R⁵¹¹, R⁵¹², R⁵¹³, R⁵¹⁴, R⁵¹⁵, R⁵¹⁶, R⁵¹⁷, R⁵¹⁸, R⁵¹⁹_(and R) ⁵²⁰ each independently represents a hydrogen atom or asubstituent, to which the aforementioned substituent T is applicable.

Also these substituents may be further substituted with anothersubstituent, or may be mutually condensed to form a cyclic structure.X⁵¹¹ and X⁵¹² have same meanings as X⁵¹ and X⁵² in the formula (5).

R⁵¹¹, R⁵¹², R⁵¹⁴, R⁵¹⁵, R⁵¹⁶, R⁵¹⁷, R⁵¹⁹ and R⁵²⁰ each is preferably ahydrogen atom, an alkyl group, an alkenyl group, an alkinyl group, anaryl group, a substituted or non-substituted amino group, an alkoxygroup, an aryloxy group, a hydroxyl group, or a halogen atom, morepreferably a hydrogen atom, an alkyl group, an aryl group, an alkyloxygroup, an aryloxy group, or a halogen atom, further preferably ahydrogen atom or an alkyl group containing 1 to 12 carbon atoms,particularly preferably a hydrogen atom or a methyl group, and mostpreferably a hydrogen atom.

R⁵¹³ and R⁵¹⁸ each is preferably a hydrogen atom, an alkyl group, analkenyl group, an alkinyl group, an aryl group, a substituted ornon-substituted amino group, an alkoxy group, an aryloxy group, ahydroxyl group, or a halogen atom, more preferably a hydrogen atom, analkyl group containing 1 to 20 carbon atoms, an amino group containing 0to 20 carbon atoms, an alkoxy group containing 1 to 12 carbon atoms, anaryloxy group containing 6 to 12 carbon atoms, or a hydroxyl group,further preferably a hydrogen atom, an alkyl group containing 1 to 12carbon atoms, or an alkoxy group containing 1 to 12 carbon atoms, andparticularly preferably a hydrogen atom.

The compounds represented by the formula (5) are more preferably thoserepresented by a following formula (5-2).

In the formula, R⁵¹³ and R⁵¹⁸ have same meanings and same preferablerange as those in the formula (5-1). X⁵¹³ represents a hydrogen atom ora substituent, to which the aforementioned substituent T is applicableand which may be substituted further with another substituent, whenpossible.

X⁵¹³ represents a hydrogen atom or a substituent, to which theaforementioned substituent T is applicable and which may be substitutedfurther with another substituent, when possible. X⁵¹³ preferablyrepresents a hydrogen atom, an alkyl group, an aryl group, a cyanogroup, a nitro group, a carbonyl group, a sulfonyl group, or an aromaticheterocycle, more preferably a cyano group, a carbonyl group, a sulfonylgroup, or an aromatic heterocycle, further preferably a cyano group or acarbonyl group, and particularly preferably a cyano group or analkoxycarbonyl group {-C(═O)}OR⁵² (R⁵² being an alkyl group containing 1to 20 carbon atoms, an aryl group containing 6 to 12 carbon atoms or acombination thereof)).

The compounds represented by the formula (5) are further preferablythose represented by a following formula (5-3).

In the formula, R⁵¹³ and R⁵¹⁸ have same meanings and same preferablerange as those in the formula (5-1). R⁵² represents an alkyl groupcontaining 1 to 20 carbon atoms. In a case that R⁵¹³ and R⁵¹⁸ are bothhydrogen atoms, R⁵² is preferably an alkyl group containing 2 to 12carbon atoms, more preferably an alkyl group containing 4 to 12 carbonatoms, further preferably an alkyl group containing 6 to 12 carbonatoms, particularly preferably an n-octyl group, a t-octyl group, a2-ethylhexyl group, an n-decyl group, or an n-dodecyl group, and mostpreferably a 2-ethylhexyl group.

In a case that R⁵¹³ and R⁵¹⁸ are other than hydrogen ztoms, R⁵² ispreferably an alkyl group providing the compound of the formula (5-3)with a molecular weight of 300 or higher and containing 20 or lesscarbon atoms.

In the invention, the compound represented by the formula (5) can besynthesized by a method described in J. Am. Chem. Soc., 63, p.3452(1941).

Specific examples of the compound represented by the formula (5) areshown below, but the present invention is not limited to those specificexamples.

The optical film of the invention may contain at least one each of thecompound reducing Rth(550) described above and the compound increasingARth which is represented by a formula (10):

ΔRth=Rth(450)−Rth(650).

(Organic Solvent for Polymer Solution)

In the invention, the producing method for the optical film is notparticularly restricted. Any known method may be usable, including amelt film forming method or a solution film forming method. The opticalfilm formed by a polymer is preferably produced by a solvent castingmethod, in which the film is produced by a solution (dope) prepared bydissolving a raw material polymer in an organic solvent. An organicsolvent preferably employed as a principal solvent in the invention ispreferably selected from an ester, a ketone or an ether, containing 3 to12 carbon atoms, and a halogenated hydrocarbon containing 1 to 7 carbonatoms. The ester, ketone and ether may have a cyclic structure. Also acompound, having any one of ester, ketone or ether functional group(namely —O—, —CO— or —COO—) in two or more units, may also be employedas a principal solvent, and it may also have another functional groupsuch as an alcoholic hydroxyl group. In case of a principal solventhaving functional groups of two or more kinds, a number of carbon atomsof such solvent may be within a range defined for a compound havingeither one of such functional groups.

For the optical film of the invention, a chlorine-containing halogenatedhydrocarbon may be employed as a principal solvent, or, as described inthe Japan Institute of Invention and Innovation, Laid-open TechnicalReport 2001-1745 (p. 12-16), a chlorine-free solvent may be employed asa principal solvent, and no particular restriction is made for theoptical film of the invention.

Also the solvents for a polymer solution and a film, usable in theoptical film of the invention, also including a solving method, aredescribed in following patent references and constitute preferableembodiments. The references include, for example, JP-A-2000-95876,JP-A-12-95877, JP-A-10-324774, JP-A-8-152514, JP-A-10-330538,JP-A-9-95538, JP-A-9-95557, JP-A-10-235664, JP-A-12-63534,JP-A-11-21379, JP-A-10-182853, JP-A-10-278056, JP-A-10-279702,JP-A-10-323853, JP-A-10-237186, JP-A-11-60807, JP-A-11-152342,JP-A-11-292988, JP-A-11-60752 and JP-A-11-60752. These referencesinclude descriptions not only on solvents preferable for the polymer ofthe invention but also on physical properties of the solvent andco-existing substances to be made present, thus providing preferableembodiments also in the present invention.

(Producing Process of Optical Film) (Dissolving Step)

Preparation of a polymer solution (dope) in the invention is notparticularly restricted in the dissolving method, and may be executed atthe room temperature, or by a cooled dissolving method, ahigh-temperature dissolving method or a combination thereof. For thepreparation of the polymer solution in the invention and a solutionconcentrating step and a filtering step associated with the dissolvingstep, a producing method described in detail in the Japan Institute ofInvention and Innovation, Laid-open Technical Report (2001-1745, issuedMar. 15, 2001), pages 22-25, may be employed advantageously.

(Transparency of Dope Solution)

The polymer solution (dope) of the invention preferably has atransparency of 85% or higher, more preferably 88% or higher, andfurther preferably 90% or higher. In the invention, it is confirmed thatvarious additives are sufficiently dissolved in the polymer dopesolution. For calculating the dope transparency, the dope solution isfilled in a glass cell of 1 cm square, and subjected to a measurement ofan absorbance at 550nm by a spectrophotometer (UV-3150, manufactured byShimadzu Corp.). A solvent alone is measured in advance as a blank, andthe transparency of the polymer solution is calculated from a ratio tothe blank absorbance.

(Casting, Drying and Winding Steps)

Then a film producing method utilizing the polymer solution of theinvention will be explained. As a method and an equipment for producingthe optical film of the invention, there are preferably employed a filmproducing method by solution casting and a film producing equipment bysolution casting, that have been used for producing a cellulosetriacetate film. A preferred embodiment of such method will be explainedbelow.

A dope (polymer solution) prepared in a dissolver (pot) is once storedin a storage pot, and is subjected to a final preparation by a defoamingof bubbles contained in the dope. The dope is fed, from a dope exit, toa pressurized die for example through a pressurized constant-rate gearpump, capable of a constant-rate feeding of a high precision by arevolution. The dope is uniformly cast, from an aperture (slit) of thepressurized die, onto a running endless metal support member, and ahalf-dried dope film (also called a web) is peeled from the metalsupport member at a peeling point after about a cycle of the metalsupport member. The obtained web is supported at both ends thereof byclips, then dried by conveying in a tenter under a maintained width,further dried by conveying with rolls in a drying apparatus, and woundin a predetermined length by a winder. A combination of the tenter andthe rolls in the drying apparatus is variable depending on the purpose.After the dope film is peeled off as a film from the metal supportmember, a step of stretching the film may be provided. In such case, itis also possible to regulate a wavelength dependence of the opticalproperties of the film, by suitably regulating a stretching temperatureand a stretching magnification. In the film forming method by solutioncasting, to be employed for producing a functional protective film as anoptical member for an electronic display, which is a principal purposeof the optical film of the invention, and for producing a silver halidephotographic material, there is often provided, in addition to the filmforming apparatus by solution casting, a coating apparatus for formingan undercoat layer, an antistatic layer, an antihalation layer, aprotective layer and the like onto the surface of the film. Thesematters are described in detail in the Japan Institute of Invention andInnovation, Laid-open Technical Report (2001-1745, issued Mar. 15,2001), pages 25-30, under items of casting (including co-casting), metalsupport member, drying, peeling etc., and may be employed advantageouslyin the present invention.

The optical film of the invention preferably has a film thickness offrom 20 to 200 μm, more preferably from 30 to 160 μm, and furtherpreferably from 40 to 120 μm.

(Stacked-Type Optical Compensation Film)

The optical film of the invention may be stacked with an opticallyanisotropic layer satisfying following relations (13) and (14):

0≦Re≦400; and  (13)

−400≦Rth≦400,  (14)

and preferably:

0≦Re≦300; and  (13′)

−300≦Rth≦300.  (14′)

In the relations (13) to (14′), Re and Rth are respectively an in-planeretardation (unit: nm) and a retardation in thickness direction (unit:nm), measured with a light of any wavelength within a visible region.The measuring wavelength is preferably from 400 to 700 nm, morepreferably from 450 to 650 nm, and most preferably from 500 to 600 nm.

In the invention, the optically anisotropic layer satisfying therelations (13) and (14) is not limited to a single-layered structure butmay have a layered structure of plural layers. In an embodiment of suchlayered structure, materials for the layers need not be same, and forexample optically anisotropic layers utilizing a discotic liquidcrystal, a cholesteric liquid crystal or a rod-shaped liquid crystal maybe employed singly or in a combination. Also a stacked member of apolymer film and an optically anisotropic layer of a liquid crystallinecompound may be utilized. In an embodiment of such layered structure, acoated-type layered member including a layer formed by coating ispreferable to a stacked member of stretched polymer films, inconsideration of the thickness.

(Optical Compensation Film Formed by a Liquid Crystal Compound)

In preparing an optically anisotropic layer meeting (13) and (14) above,and in case of utilizing a liquid crystalline compound for thepreparation of such optically anisotropic layer, since the liquidcrystalline compound involves various alignment states, an opticallyanisotropic layer prepared by fixing the liquid crystalline compound ata specified alignment state can exhibit a desired optical property, by asingle layer or by a layered member of plural layers. Thus, theoptically anisotropic layer may assume an embodiment formed by asubstrate and one or more optically anisotropic layers formed thereon.In such embodiment, a retardation of the entire optically anisotropiclayer may be regulated by an optical anisotropy of the opticallyanisotropic layer. The liquid crystalline compounds are classified,according to a molecular shape thereof, into a discotic liquid crystal,a cholesteric liquid crystal and a rod-shaped liquid crystal. Eachincludes a low-molecular type and a high-molecular type, each of whichis usable.

(Optically Anisotropic Layer Formed by Polymer Film)

As described above, the optically anisotropic layer may be formed by apolymer film. The polymer film is formed from a polymer capable ofexpressing an optical anisotropy. Examples of such polymer includepolyolefin (such as polyethylene, polypropylene or norbornene-typepolymer), polycarbonate, polyallylate, polysulfone, polyvinyl alcohol,polymethacrylate ester, pobiactylate ester and cellulose ester (such ascellulose triacetate or cellulose diacetate). Also a copolymer or amixture of these polymers may be employed.

The optical anisotropy of the polymer film is preferably obtained bystretching. The stretching is preferably executed by a monoaxialstretching method or a biaxial stretching method. More specifically, alongitudinal monoaxial stretching utilizing a peripheral speeddifference in two or more rolls, a tenter stretching in which thepolymer film is gripped on both sides and stretched in the transversaldirection, or a biaxial stretching by combining these, is preferable.Also it is possible to utilize two or more polymer films in such amanner that the entire optical properties of two or more films satisfythe aforementioned conditions. The polymer film is preferably producedby a solvent cast method, in order to reduce an unevenness in thebirefringence. The polymer film preferably has a thickness of from 20 to500 μm, and most preferably from 40 to 100 μm.

Also there is advantageously employed a method of forming a polymer filmconstituting the optically anisotropic layer, by utilizing at least apolymer material selected from a group of polyamide, polyimide,polyester, polyether ketone, polyamidimide, polyesterimide, andpolyallyl ether ketone, coating a solution prepared by dissolving suchpolymer material in a solvent on a substrate and drying the solvent toobtain a film. In such case, a method of laminating the polymer film anda base material and then stretching both together to express an opticalanisotropy as an optically anisotropic layer is also employableadvantageously, and the optical film of the invention is preferablyemployed as the base material. It is also preferable to prepare thepolymer film on another base material, then peeling the polymer from thebase material and adhere it with the optical film of the invention, asan optically anisotropic layer. Such method allows to reduce thethickness of the polymer film, which is preferably 50 μm or less andmore preferably from 1 to 20 μm.

(Surface Treatment)

The optical film of the invention may be subjected to a surfacetreatment, in certain cases, for achieving an improved adhesion betweenthe optical film and functional layers (for example an undercoat layerand a back layer). The surface treatment can be executed for example bya glow discharge treatment, an ultraviolet irradiation treatment, acorona treatment, a flame treatment, or an acid or alkali treatment. Theglow discharge treatment can be executed with a low-temperature plasmagenerated in a low-pressure gas of 10⁻-20 Torr, or can also beadvantageously executed by a plasma treatment under an atmosphericpressure. A plasma exciting gas means a gas capable of exciting a plasmaunder the aforementioned condition, and can be argon, helium, neon,krypton, xenon, nitrogen, carbon dioxide, a fluorinated gas such astetrafluoromethane or a mixture thereof. Details of such materials aredetailedly described in Japan Institute of Invention and Innovation,Laid-open Technical Report (2001-1745, issued Mar. 15, 2001, JIII),pages 30-32, and may be advantageously utilized in the invention.

(Contact Angle of Film Surface by Alkali Saponification Treatment)

In case of utilizing the optical film of the invention as a transparentprotective film for a polarizing plate, an effective surface treatmentis an alkali saponification treatment. In such case, the film surfaceafter the alkali saponification treatment preferably has a contact angleof 55° or less, more preferably 50° or less and further preferably 45°or less. The contact angle can be evaluated by an ordinary method ofdropping a water drop of a diameter of 3 mm onto the film surface afterthe alkali saponification treatment and measuring an angle formed by thefilm surface and the water drop, and can be used as an evaluation ofhydrophilicity.

(Polarizing Plate)

The optical film of the invention is preferably employable as aprotective film of a polarizing plate. In case of use as a protectivefilm of a polarizing plate, the polarizing plate is not particularlyrestricted in a producing method and can be prepared by an ordinaryproducing method. For example there is known a method of alkali treatingan obtained optical film and adhering such optical film, with an aqueoussolution of a completely saponified polyvinyl alcohol, on both sides ofa polarizer prepared by dipping and stretching a polyvinyl alcohol filmin an iodine solution. Instead of alkali treatment, there may beemployed an adhesion promoting treatment as described in JP-A Nos.6-94915 and 6-118232.

An adhesive to be employed for adhering a treated surface of theprotective film and the polarizer can be, for example, a polyvinylalcohol-type adhesive such as polyvinyl alcohol or polyvinyl butyral, ora vinylic latex such as butyl acrylate.

The polarizing plate is constituted of a polarizer and protective filmsfor protecting both sides thereof, and a protecting film and aseparation film may be adhered respectively on one side and the otherside of such polarizing plate. The protecting film and the separationfilm are used for the purpose of protecting the polarizing plate at ashipping or a product inspection of the polarizing plate. In such case,the protecting film is adhered for the purpose of protecting a surfaceof the polarizing plate, opposite to the side of the polarizing plateadhered to a liquid crystal panel, while the separation film is employedfor the purpose of covering an adhesive layer for adhesion to the liquidcrystal panel, on a side of the polarizing plate to be adhered to theliquid crystal panel.

A liquid crystal display usually includes substrates, containing liquidcrystal, between two polarizing plates, and the polarizing plateprotective film, utilizing the optical film of the invention, may beutilized in any position. For the purpose of the present invention forachieving an optical compensation in all the visible wavelength range,it is effective and preferable to utilize the optical film of theinvention as a polarizing plate protecting film at the side of theliquid crystal cell.

(Polarizing Plate Integral with Optical Compensation Film)

In case of utilizing the optical film of the invention as an opticalcompensation film, for example in case of coating or adhering anoptically anisotropic layer on one side of the optical film of theinvention, it is possible to adhere the optical compensation film, withan adhesive, to a polarizing plate already prepared by adheringprotective films on both sides of a polarizer, or to execute a surfacetreatment on the optical film of the invention, on a side thereof notcoated or adhered with the optically anisotropic layer and to adheresuch optical film directly to the polarizer. In such case, for example apolyvinyl alcohol-based polarizing plate is not restricted in aproducing method and may be prepared by an ordinary method. For example,there may be employed a method of executing a surface modification on asurface the optical film by an alkali saponification treatment, a plasmatreatment or a corona discharge treatment, and applying such opticalfilm on both surfaces of a polarizer prepared by dipping and stretchinga polyvinyl alcohol (PVA) film in an iodine solution.

(Functional Layer)

In case of utilizing the optical film of the invention as a protectivefilm of a polarizing plate in a liquid crystal display, variousfunctional layers may be provided on the surface. These include, forexample, a cured resin layer (transparent hard coat layer), an antiglarelayer, an antireflective layer, an adhesion promoting layer, an opticalcompensation layer, an alignment layer and an antistatic layer forliquid crystal layer. These functional layers in which the optical filmof the invention is applicable, and materials therefor include forexample a surfactant, a lubricant, a matting agent, an antistatic layerand a hard coat layer, which are described in detail in Japan Instituteof Invention and Innovation, Journal of Technical Disclosure (No.2001-1745, issued Mar. 15, 2001, JIII), p. 32-45, and are advantageouslyemployable in the invention.

(Liquid Crystal Display)

A liquid crystal display of the present invention an optical film(optical compensation film), a liquid crystal cell and polarizing platesin combination. The optical film (optical compensation film), the liquidcrystal cell and the polarizing plates are preferably contacted closely,and a tacky material or an adhesive material already known may beemployed for such close contact.

The optical film of the invention, and the optical compensation film orthe polarizing plate utilizing the same may be applied to liquid crystaldisplays of various display modes. Representative display modes proposedinclude VA (vertically aligned), IPS (in-plane switching), TN (twistednematic), OCB (optically compensatory bend), STN (super twistednematic), ECB (electrically controlled birefringence), FLC(ferroelectric liquid crystal), AFLC (anti-ferroelectric liquidcrystal), and HAN (hybrid aligned nematic). Also there is proposed adisplay mode with an alignment division in the above-mentioned displaymodes. Effects obtained by the optical film of the invention areconspicuous particularly in a liquid crystal display of a large imagesize, so that it is particularly preferable to utilize the optical filmof the invention in the liquid crystal display of VA mode, IPS mode orOCB mode, utilized in large-size televisions.

The optical film of the invention is preferably employed in a displaymode in which the liquid crystal molecules are vertically aligned in ablack display state, such as VA mode, a display mode in which the liquidcrystal molecules are parallel aligned in a black display state, such asIPS or FFS mode, and an OCB mode in which the liquid crystal moleculesare bend aligned.

For example, in case of utilizing at least either of the optical film,the optical compensation film and the polarizing plate of the inventionin a liquid crystal display, the liquid crystal display may include atleast an optically anisotropic layer. Such optically anisotropic layerpreferably satisfies following relations (15) and (16):

0≦Re≦400; and

−400≦Rth≦400.  (16)

In the relations (15) and (16), Re and Rth are respectively an in-planeretardation (unit: nm) and a retardation in thickness direction (unit:nm), measured with a light of any wavelength within a visible region.The measuring wavelength is preferably from 400 to 700 nm, morepreferably from 450 to 650 nm, and most preferably from 500 to 600 mm.

The optically anisotropic layer is not limited to a single-layerstructure, but may have a layered structure formed by laminating plurallayers. In an embodiment of such layered structure, materials for thelayers need not be same, and for example optically anisotropic layersutilizing a discotic liquid crystal, a cholesteric liquid crystal or arod-shaped liquid crystal may be employed singly or in a combination.Also a laminated member of a polymer film and an optically anisotropiclayer of a liquid crystalline compound may be utilized. In an embodimentof such layered structure, a coated-type layered member including alayer formed by coating is preferable to a laminated member of stretchedpolymer films, in consideration of the thickness.

The optically anisotropic layer may be those cited in the explanation ofthe laminated optical compensation film.

When the liquid crystal display includes a liquid crystal cell in whichthe liquid crystal molecules are vertically aligned in a black displaystate, in order to obtain viewing angle chracteristics showing littlelight leakage and little color shift in the inclined direction, theapparatus preferably includes at least an optically anisotropic layersatisfying 10≦Re≦150 and 50≦Rth≦400. Such optically anisotropic layermore preferably satisfies 20≦Re≦120 and 60≦Rth 350, and most preferably30≦Re≦100 and 80≦Rth≦300.

When the liquid crystal display includes a liquid crystal cell in whichthe liquid crystal molecules are parallel aligned in a black displaystate, in order to obtain viewing angle chracteristics showing littlelight leakage and little color shift in the inclined direction, theapparatus preferably includes at least an optically anisotropic layersatisfying either one of relations (19) to (22). A more preferableembodiment of the liquid crystal display of the invention includes anoptically anisotropic layer satisfying the relation (20) and anoptically anisotropic layer satisfying the relation (21). Anotherfurther preferable embodiment includes an optically anisotropic layersatisfying the relation (20) and an optically anisotropic layersatisfying the relation (22):

100≦Re≦400, and −50≦Rth≦50;  (19)

0≦Re≦20, and −400≦Rth≦−50;  (20)

60≦Re≦200, and 20≦Rth≦120;  (21)

30≦Re≦150, and 100≦Rth≦400.  (22)

When the liquid crystal display includes a liquid crystal cell in whichthe liquid crystal molecules are bend aligned in a black display state,in order to obtain viewing angle chracteristics showing little lightleakage and little color shift in the inclined direction, the apparatuspreferably includes at least an optically anisotropic layer containing adiscotic liquid crystal compound. An alignment state of the discoticliquid crystal compound is preferably such that a disk face is inclinedwith respect to the surface of the optically anisotropic layer, and morepreferably is a hybrid alignment in which an angle of such inclinationchanges along the thickness direction of the optically anisotropiclayer.

In each optically anisotropic layer, Re and Rth are respectively anin-plane retardation (unit: nm) and a retardation in thickness direction(unit: nm), measured with a light of any wavelength within a visibleregion. The measuring wavelength is preferably from 400 to 700 nm, morepreferably from 450 to 650 nm, and most preferably from 500 to 600 nm.

EXAMPLES

In the following, the present invention will be further clarified byexamples, but the present invention is not limited to such examples.

In executing the present invention, in case of employing celluloseacylate as a polymer material as a reference for selecting the rawmaterial, it is found that a larger acyl substitution degree iseffective for reducing the retardation. Rth(550) as a function of acylsubstitution degree of cellulose triacetate is shown in FIG. 9.

Also in the present invention, it is found that, as one of additives forcontrolling the optical characteristics of the optical film of theinvention, a larger amount of the Rth reducing agent is effective forreducing the retardation of the film. Rth(550) as a function of theamount of compound 119 is shown in FIG. 10.

Also in the present invention, it is found that, as one of additives forcontrolling the optical characteristics of the optical film of theinvention, a larger amount of the wavelength-dependent dispersionregulating agent is effective for increasing ΔRth of the film. Rth(550)as a function of the amount of compound UV102 is shown in FIG. 11.

In the optical film of the invention, a kind of the polymer material,and kinds and amounts of the additives for controlling the opticalcharacteristics were suitably selected. FIGS. 9 to 11 show mereexamples, and the effects are variable depending for example on thecombination of materials, but these concepts were employed as designprinciples for preparing the optical film.

In the present example, the compounds indicated as the Rth reducingagent and the wavelength-dependent dispersion regulating agent are thosedescribed in the specification.

Example 1

(Preparation of Cellulose Acylate Solution CA-1)

A following composition was charged in a mixing tank, and agitated todissolve components thereby obtaining a cellulose acylate solution CA-1.

(Composition of Cellulose Acylate Solution CA-1)

cellulose acylate with Ac substitution degree: 2.92 100.0 parts byweight Rth reducing agent: compound 119  14.0 parts by weight methylenechloride (1st solvent) 402.0 parts by weight methanol (2nd solvent) 60.0 parts by weight

(Preparation of Matting Agent Solution MT-1)

20 parts by weight of silica particles of an average particle size of 16nm (AEROSII, R972, manufactured by Nippon Aerosil Co.) and 80 parts byweight of methanol were well mixed under agitation for 30 minutes toobtain a silica particle dispersion. The dispersion was charged in adisperser together with the following composition and agitated for 30minutes or longer to dissolve the components, thereby obtaining amatting agent solution MT-1.

(Composition of Matting Agent Solution MT-1)

dispersion of silica particles of average particle 10.0 parts by weightsize: 16 nm methylene chloride (1st solvent) 76.3 parts by weightmethanol (2nd solvent)  3.4 parts by weight cellulose acylate solutionCA-1 10.3 parts by weight

(Preparation of Additive Solution)

Following composition was charged in a mixing tank and agitated underheating to dissolve the components, thereby obtaining an additivesolution AD-1.

(Composition of Additive Solution AD-1)

wavelength-dependent dispersion regulating agent:  7.6 parts by weightUV-208 methylene chloride (1st solvent) 58.4 parts by weight methanol(2nd solvent)  8.7 parts by weight cellulose acylate solution CA-1 12.8parts by weight

(Preparation of Optical Film Sample 001)

94.6 parts by weight of the cellulose acylate solution CA-1, 1.3 partsby weight of the matting agent solution MT-1, and 2.3 parts by weight ofthe additive solution AD-1, after each being filtered, were mixed andcast by a band casting machine. In the above-described composition, theRth reducing agent and the wavelength-dependent dispersion regulatingagent had weight ratios, with respect to cellulose acylate, respectivelyof 14.0% and 1.0%. A prepared film with a residual solvent amount of 30%was peeled off from the band, and was dried at 135° C. for 20 minutes toobtain a cellulose acylate film. The completed optical film 001 had aresidual solvent amount of 0.2% and a film thickness of 80 μm.

The prepared film was subjected to a moisture adjustment for 2 hours ormore in an environment of 25° C. and 60% RH, and was subjected to ameasurement of three-dimensional birefringence with an autobirefringence meter KOBRA 21ADH (manufactured by Oji ScientificInstruments Ltd.) at wavelengths of 450, 550 and 650 nm in anenvironment of 25° C. and 60% RH, to obtain an in-plane retardation Reand a retardation Rth in the thickness direction, obtained by Remeasurements at different inclination angles, thereby obtaining opticalcharacteristics shown in Table 4.

Example 2

An optical film 002, having a thickness of 80 μm and opticalcharacteristics shown in Table 4, was obtained in the same manner as inExample 1, except that the amount of the compound 119 in the celluloseacylate solution CA-1 in Example 1 was changed to 12.0 parts by weightand the amount of UV-208 in the additive solution AD-1 was changed to3.0 parts by weight.

Example 3

An optical film 003, having a thickness of 80 μm and opticalcharacteristics shown in Table 4, was obtained in the same manner as inExample 1, except that the amount of the compound 119 in the celluloseacylate solution CA-1 in Example 1 was changed to 10.0 parts by weightand the amount of UV-208 in the additive solution AD-1 was changed to1.5 parts by weight.

Example 4

An optical film 004, having a thickness of 80 μm and opticalcharacteristics shown in Table 4, was obtained in the same manner as inExample 1, except that UV-208 in the additive solution AD-1 in Example 1was changed to UV-20.

Example 5

An optical film 005, having a thickness of 80 μm and opticalcharacteristics shown in Table 4, was obtained in the same manner as inExample 1, except that UV-208 in the additive solution AD-1 in Example 1was changed to UV-3.

Example 6

An optical film 006, having a thickness of 80 μm and opticalcharacteristics shown in Table 4, was obtained in the same manner as inExample 1, except that the amount of the compound 119 in the celluloseacylate solution CA-1 in Example 1 was changed to 16.0 parts by weight,that UV-208 in the additive solution AD-1 was changed to UV-3 and thatthe amount of UV-3 was changed to 15.2 parts by weight.

Example 7

An optical film 007, having a thickness of 80 μm and opticalcharacteristics shown in Table 4, was obtained in the same manner as inExample 1, except that the amount of UV-3 in the additive solution inExample 6 was changed to 12.2 parts by weight.

Example 8

An optical film 008, having a thickness of 80 μm and opticalcharacteristics shown in Table 4, was obtained in the same manner as inExample 1, except that the amount of the compound 119 in the celluloseacylate solution CA-1 in Example 1 was changed to 12.0 parts by weight,that UV-208 in the additive solution AD-1 was changed to UV-102 and thatthe amount of UV-102 was changed to 9.1 parts by weight.

Comparative Example 1

As a comparative example, a commercially available cellulose acylatefilm FUJITAC TD80UL (film thickness 80 μm, manufactured by Fuji PhotoFilm Co.) was prepared. This film had optical characteristics as shownin Table 4.

Comparative Example 2

As a comparative example, a commercially available cycloolefin filmZeonor ZF-14 (film thickness 100 manufactured by Nippon Zeon Ltd.) wasprepared. This film had optical characteristics as shown in Table 4.

TABLE 4 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Comp. Ex. 1Comp. Ex. 2 sample name 001 002 003 004 005 006 007 008 TD80UL ZF-14 rawmaterial polymer Ac2.92 Ac2.92 Ac2.92 Ac2.92 Ac2.92 Ac2.92 Ac2.92 Ac2.92— Zeonor Rth reducing agent 119 119 119 119 119 119 119 119 — — (wt %)(14%) (12%) (10%) (14%) (14%) (16%) (16%) (12%) wavelength-dependentdispersion UV-208 UV-208 UV-208 UV-208 UV-3 UV-3 UV-3 UV-102 — — reg.agent (wt %) (1.0%) (0.4%) (0.2%) (1.0%) (1.0%) (2.0%) (1.6%) (1.2%)Re(nm) 450 1.0 −3.2 −9.5 −5.3 1.3 5.3 5.8 5.3 −0.8 6.1 550 1.0 1.0 0.80.8 1.2 1.2 1.0 1.0 2.9 6.0 650 1.0 5.1 6.8 5.3 1.2 −1.6 −3.2 −1.8 5.06.0 I = 450-550 0.0 −4.2 −10.3 −6.1 0.1 4.1 4.8 4.3 −3.7 0.1 II =650-550 0.0 4.1 6.0 4.5 0.0 −2.8 −4.2 −2.8 2.1 0.0 Rth(nm) 450 −10.5−8.0 −0.4 5.6 9.3 8.3 −1.9 −13.2 32.8 6.8 550 0.5 0.4 −0.5 −0.7 2.0 2.1−1.8 −2.0 42.4 6.9 650 7.7 7.3 −0.5 −3.2 −1.3 −3.5 −1.8 2.8 48.5 6.9 III= 450-550 −11.0 −8.4 0.1 6.3 7.3 6.2 −0.1 −11.2 −9.6 −0.1 IV = 650-5507.2 6.9 0.0 −2.5 −3.3 −5.6 0.0 4.8 6.1 0.0 |I| + |II| + |III| + |IV|18.2 23.6 16.4 19.4 10.7 18.7 9.1 23.1 21.5 0.2 class (Tabs. 2, 3) A A BB C C D D — — case (Tables 2, 3) (1) (2) (3) (4) (5) (6) (7) (8) — — Ex.10A (VA color shift) (+) (+) (−) (−) Ex. 10B (VA color shift) (+) (+)(−) (−) Ex. 10C (VA color shift) (+) (+) (−) (−) Ex. 10D (VA colorshift) (+) (+) (−) (−) Ex. 11 (IPS color shift) (+) (−) Ex. 12A (IPSview angle) (+) (−) (−) Ex. 12B (IPS view angle) (+) (−) (−) Ex. 12C(IPS view angle) (+) (−) (−) Ex. 12D (IPS view angle) (+) (−) (−) Ex. 13(OCB color shift) (+) (±) (−)

Example 9

(Working of Polarizing Plate)

(Preparation of Polarizing Plate)

Surfaces of the optical film 001 of the invention were subjected to analkali saponification process. It was immersed in a 1.5N aqueoussolution of sodium hydroxide at 55° C. for 2 minutes, then rinsed in awater rinsing tank of room temperature, and was neutralized with 0.1Nsulfuric acid of 30° C. It was rinsed again in a water rinsing tank ofroom temperature, and was dried with warm air of 100° C. Then a rolledpolyvinyl alcohol film of a thickness of 80 μm was continuouslystretched 5 times in an aqueous solution of iodine and dried to obtain apolarizing film of a thickness of 20 μm. The alkali-saponified opticalfilm 001 and a similarly alkali-saponified FUJITAC TD80UL (manufacturedby Fuji Photo Film Co.) were prepared and adhered, utilizing a 3%aqueous solution of polyvinyl alcohol (PVA-117H, manufactured by KurarayCo.) as an adhesive, with the polarizing film therebetween, in such amanner that the alkali-saponified surfaces are at the side of thepolarizing film, thereby obtaining a polarizing plate 101 in which theoptical film 001 and TD80UL constitute protective films of thepolarizing film. The adhesion was made in such a manner that the phaseretarding axes of the optical film 001 and TD80UL are parallel to theabsorption axis of the polarizing film. Similarly the optical films002-008 of the invention were used to prepare polarizing plates, whichwill be hereinafter called polarizing plates 102-108. These polarizingplates had sufficient polarizing ability.

Also TD80UL of Comparative Example 1 was used, in a similar manner, toprepare a polarizing plate 201. The polarizing plate 201 is a polarizingplate protected on both sides by TD80UL. Also Zeonor film ZF-14 ofComparative Example 2 was subjected to a corona discharge treatment as asurface treatment instead of alkali saponification, and was otherwiseprocessed similarly to obtain a polarizing plate 202. These polarizingplates 201, 202 had a sufficient polarizing ability.

Example 10

(Mounting on VA Panel)

Evaluation of mounting on a VA panel was conducted in following fourclasses A to D, according to the type of the optical characteristics ofthe optical compensation film employed on the liquid crystal display.

(Class A)

The optical film of the invention was evaluated by mounting on a liquidcrystal display of VA mode. A VA-mode liquid crystal television(LC-20C5, manufactured by Sharp Inc.) was used, after removing the frontand rear polarizing plates and the retardation plate, as a liquidcrystal cell for mounting. A polarizing film was prepared in the samemanner as in Example 9. An optical compensation film 4-A, subjected to asaponification treatment on a surface, was adhered on a surface of thepolarizing film, and a cellulose triacetate film (FUJITAC TD80UL,manufactured by Fuji Photo Film Co.), subjected to a saponificationtreatment on a surface, was adhered on the other surface of thepolarizing film, utilizing a polyvinyl alcohol-based adhesive, therebyobtaining a polarizing plate 4-A. The optical characteristics of theoptical compensation film 4-A are shown in Table 5. In a structure shownin FIG. 5, there were employed the polarizing plate 4-A as an opticalcompensation film 4 and a polarizing plate 1, the aforementioned VA-modeliquid crystal cell as a liquid crystal cell 3, and the polarizing plate101 prepared in Example 9 as an optical film 5 and a polarizing plate 2,and these were adhered with a tacky adhesive material. The adhesion wasmade in such a manner that the optical compensation film 4-A of thepolarizing plate 4-A was positioned at the side of the liquid crystalcell, and that the optical film 001 of the polarizing plate 101 waspositioned at the side of the liquid crystal cell. The adhesion was alsomade in such a manner that a phase retarding axis of the opticalcompensation film 4-A was perpendicular to the absorbing axis of thepolarizing plate 1. Also a mounting was executed by adhering each of thepolarizing plate 102 obtained in Example 9, and the polarizing plate 201and 202 utilizing Comparative Example 1 and 2, in combination with theoptical compensation film 4-A shown in Table 5.

TABLE 5 wavelength (nm) Re (nm) Rth (nm) 450 48 264 550 75 228 650 91217

(Class B)

In a structure similar to that of Example 10 (class A), a mounting wasexecuted by employing the polarizing plate 103, 104, 201 or 202 insteadof the polarizing plate 101, and employing an optical compensation film4-B of the optical characteristics shown in Table 6 instead of theoptical compensation film 4-A.

TABLE 6 wavelength (nm) Re (nm) Rth (nm) 450 45 215 550 59 242 650 62258

(Class C)

In a structure similar to that of Example 10 (class A), a mounting wasexecuted by employing the polarizing plate 105, 106, 201 or 202 insteadof the polarizing plate 101, and employing an optical compensation film4-C of the optical characteristics shown in Table 7 instead of theoptical compensation film 4-A.

TABLE 7 wavelength (nm) Re (nm) Rth (nm) 450 68 242 550 63 224 650 61217

(Class D)

In a structure similar to that of Example 10 (class A), a mounting wasexecuted by employing the polarizing plate 107, 108, 201 or 202 insteadof the polarizing plate 101, and employing an optical compensation film4-D of the optical characteristics shown in Table 8 instead of theoptical compensation film 4-A.

TABLE 8 wavelength (nm) Re (nm) Rth (nm) 450 73 205 550 65 228 650 63234

The optical compensation films 4-A, 4-B, 4-C and 4-D shown in Tables 5-8were prepared in the following manner.

(Preparation of Optical Compensation Film)

(Preparation of Cellulose Acylate Solution CA-2)

A following composition was charged in a mixing tank, and agitated todissolve components thereby obtaining a cellulose acylate solution CA-2.

(Composition of Cellulose Acylate Solution CA-2)

cellulose acylate with Ac substitution degree: 2.81 100.0 parts byweight TPP (triphenyl phosphate)  7.8 parts by weight BDP(biphenyldiphenyl phosphate)  3.9 parts by weight methylene chloride(1st solvent) 402.0 parts by weight methanol (2nd solvent)  60.0 partsby weight

(Preparation of Matting Agent Solution MT-2)

20 parts by weight of silica particles of an average particle size of 16nm (AEROSIL R972, manufactured by Nippon Aerosil Co.) and 80 parts byweight of methanol were well mixed under agitation for 30 minutes toobtain a silica particle dispersion. The dispersion was charged in adisperser together with the following composition and agitated for 30minutes or longer to dissolve the components, thereby obtaining amatting agent solution MT-2.

(Composition of Matting Agent Solution MT-2)

dispersion of silica particles of average particle 10.0 parts by weightsize: 16 nm methylene chloride (1st solvent) 76.3 parts by weightmethanol (2nd solvent)  3.4 parts by weight cellulose acylate solutionCA-2 10.3 parts by weight

(Preparation of Additive Solution)

Following composition was charged in a mixing tank and agitated underheating to dissolve the components, thereby obtaining an additivesolution AD-2.

(Composition of additive solution AD-2) 11.5 parts by weight followingretardation expressing agent X methylene chloride (1st solvent) 58.4parts by weight methanol (2nd solvent)  8.7 parts by weight celluloseacylate solution CA-2 12.8 parts by weight Retardation expressing agentX

(Preparation of Cellulose Acylate Film Sample 401)

94.6 parts by weight of the cellulose acylate solution CA-2, 1.3 partsby weight of the matting agent solution MT-2, and 2.3 parts by weight ofthe additive solution AD-2, after each being filtered, were mixed andcast by a band casting machine. In the above-described composition, theretardation expressing agent had a weight ratio, with respect tocellulose acylate, of 1.0%. A prepared film with a residual solventamount of 30% was peeled off from the band, and was dried at 140° C. for40 minutes to obtain a cellulose acylate film. The completed celluloseacylate film 401 had a residual solvent amount of 0.2% and a filmthickness of 140 μm.

(Preparation of Optical Compensation film 4-A)

The cellulose acylate film 401 obtained above was fed to a stretchingapparatus, including a step of stretching a continuous web film in atransversal direction by means of a tenter of a structure in which alongitudinal pitch of tenter clips becomes narrower in the course ofholding and conveying of the film, and, a stretching was started aftersetting the film temperature at 180° C. and at 30 seconds after passinga heating zone, for contracting the film under relaxation by 0.72 timesin the longitudinal direction and for stretching the film by 1.23 timesin the transversal direction by means of the tenter clips, therebyobtaining an optical compensation film 4-A having a thickness of 182 μmafter the stretching.

(Preparation of Optical Compensation Film 4-B)

A process was executed in the same manner as in the preparation of theoptical compensation film 4-A, except that the cellulose acetate of Acsubstitution degree of 2.81, in the composition of the cellulose acylatesolution CA-2, was replaced by cellulose acetate of Ac substitutiondegree of 2.92, thereby obtaining a cellulose acylate film sample 402.It was used in a process similar to that for preparing the opticalcompensation film 4-A to obtain an optical compensation film 4-B.

(Preparation of Optical Compensation Film 4-C)

A process was executed in the same manner as in the preparation of theoptical compensation film 4-A, except that the cellulose acetate of Acsubstitution degree of 2.81, in the composition of the cellulose acylatesolution CA-2, was replaced by cellulose acetate of Ac substitutiondegree of 2.86, thereby obtaining a cellulose acylate film sample 403.It was subjected to a fixed biaxial stretching, which was started aftersetting the film temperature at 180° C. and at 30 seconds after passinga heating zone, to stretch the film by 1.2 times in the longitudinaldirection and by 1.1 times in the transversal direction, therebyobtaining an optical compensation film 4-C having a thickness of 180 μmafter the stretching.

(Preparation of Optical Compensation Film 4-D)

A process was executed in the same manner as in the preparation of theoptical compensation film 4-A, except that the amount of the retardationexpressing compound X in the composition of the additive solution AD-2,was changed from 11.5 parts by weight to 8.6 parts by weight, therebyobtaining a cellulose acylate film sample 404. It was subjected to afixed biaxial stretching, which was started after setting the filmtemperature at 180° C. and at 30 seconds after passing a heating zone,to stretch the film by 1.2 times in the longitudinal direction and by1.1 times in the transversal direction, thereby obtaining an opticalcompensation film 4-D having a thickness of 180 μm after the stretching.

(Evaluation of Viewing Angle-Dependent Color of Panel)

Each of the mounted VA-mode panels prepared in (class A) to (class D)above was used as a liquid crystal display of the structure shown inFIG. 5, with a backlight provided at the side of the polarizing plate 1,and, for each sample, a color shift in an inclined direction with anazimuthal angle of 45° and a polar angle of 60° in a black image displaystate. Results are shown in Table 4. In the color evaluation, a casewithout any color shift (yellowish or reddish color) is represented by(+), while a case, where a color shift is observed at a polar angle of60° but is removed when the polar angle is reduced from 60° to 30°, isrepresented by (±), and a case where a color shift is observed at anypolar angle is represented by (−). Results are shown in Table 4. Any ofthe samples prepared in Examples utilizing the optical films 001-008 ofthe invention did not show a color shift nor a light leakage whenobserved in an inclined direction. On the other hand, in liquid crystalpanels utilizing the films of Comparative Examples 1 and 2, a lightleakage was observed in an observation from an inclined direction, and acoloration (slightly reddish) in the leaking light was confirmed. Thisis because the optical characteristics Re, Rth of TD80UL in ComparativeExample 1, particularly a large absolute value of Rth, do not provide asufficient optical compensation. Also Zeonor ZF-14 in ComparativeExample 2 lacks wavelength dependence in contrast to the optical film ofthe invention, so that the polarized lights of wavelengths of R, G andB, having moved to different points after passing the liquid crystalcell as shown in FIG. 6, cannot be matched by the optical film 5 shownin FIG. 5. Measurements were also made in a white image display state todetermine a contrast ratio to the black display state, and it wasconfirmed that the optical films of the invention had an excellentcontrast ratio.

Based on the foregoing, it was confirmed that the optical film of theinvention, having desired Re and Rth, was capable of suppressing a colorshift and had a high contrast ratio over a wide range, and that thepolarizing plate and the liquid crystal display, utilizing the same hadexcellent performance.

Example 11

(Mounting on IPS Panel)

In a structure shown in FIG. 2, there were employed the polarizing plate108 prepared in Example 9 as a polarizing plate 1, the polarizing plate201 prepared in Example 9 as a polarizing plate 2, and a commercialIPS-mode liquid crystal cell as a liquid crystal cell 3, and these wereadhered with a tacky adhesive material to prepare a liquid crystaldisplay (IPS-1). In this operation, the liquid crystal cell was adheredwith the side of the optical 008 of the polarizing plate 108. Also thetransmission axes of the upper and lower polarizing plates were madeperpendicular each other, and the transmission axis of the upperpolarizing plate was made parallel to the direction of the molecularlonger axis of the liquid crystal cell (namely the phase retarding axisof the optical compensation layer and the direction of the molecularlonger axis of the liquid crystal cell being perpendicular each other).The liquid crystal cell, electrodes and substrates may be those used inthe prior IPS mode. The liquid crystal cell had a horizontal alignment,and the liquid crystal had a positive dielectric anisotropy. As anexample, a liquid crystal cell, obtained by removing polarizing platesand other components from a commercial IPS-mode liquid crystaltelevision (TH-32LX500, manufactured by Matsushita Electric IndustrialCo.), may be employed advantageously.

As a Comparative Example, a liquid crystal display (IPS-2) was prepared,in a structure shown in FIG. 2, employing the polarizing plate 201repared in Example 9 as polarizing plates 1 and 2, and the commercialIPS-mode liquid crystal cell as a liquid crystal cell 3, and adheringthese with a tacky adhesive material.

On thus prepared liquid crystal display IPS-1 and IPS-2, a light leakrate in a black display state was measured in an evaluation methodsimilar to that in Example 10 and in a direction of an azimuthal angleof 45° and a polar angle of 60° from a frontal direction to theapparatus. Results are shown in Table 4. The liquid crystal displayIPS-1, employing the polarizing plate 108 utilizing the optical film ofthe invention, showed little light leakage and no color shift in theobservation from the inclined direction, while the liquid crystaldisplay IPS-2, employing the polarizing plate 201 utilizing the opticalfilm of Comparative Example 1, showed a light leakage and a color shift.It was also found that IPS-1 was superior in the viewing angle propertyof contrast.

The Example 11 and Comparative Example are represented, on a Poincaresphere, as shown in FIGS. 12 and 13. In FIG. 12, T_(in) indicates anincident light at the side of the polarizing plate 1, and P_(out)indicates an emergent light at the side of the polarizing plate 2. As anideal point for the emergent light is A_(out), a smaller distancebetween P_(out) and A_(out) is closer to the ideal state. This distancecorresponds to the light leakage in the black display state. In FIG. 13,a movement from T_(in) to P₁ is caused by the retardation of the film ofComparative Example, employed in the polarizing plate 201. Also amovement from P₁ to P₂ is an arc about A_(out), caused by theretardation of the liquid crystal cell. Also a movement from P₂ toP_(out) is caused by the retardation of the film of Comparative Example,employed in the polarizing plate 2. On the other hand, in FIG. 12, thereis scarce movement from T_(in) to P₁, because the optical film 108 ofthe invention has scarce retardation. Because of this fact, the movementfrom P₁ to P₂ has a smaller arc radius, whereby the distance betweenP_(out) and A_(out) becomes smaller than in the case of FIG. 13. Thisfact also explains the smaller light leakage in case of employing theoptical film of the invention.

Example 12

(Preparation of Optical Compensation Film 5-A)

A solution containing cellulose acylate was prepared in the same manneras in Example 10. 100 parts by weight of the cellulose acylate solutionCA-2 and 1.3 parts by weight of the matting agent solution MT-2 weremixed, and the additive solution AD-2 was mixed in such a manner thatthe retardation expressing agent X was present in 6 parts by weight,with respect to 100 parts by weight of cellulose acetate, therebyobtaining a film forming dope.

The obtained dope was cast with a casting machine, having a band of awidth of 2 in and a length of 65 m. A film with a residual solventamount of 15 wt % was transversally stretched by a tenter with astretching magnification of 20% under a condition of 130° C., thenmaintained at a width after stretching for 30 seconds at 50° C. and thenunclipped to obtain a cellulose acetate film. After the stretching, itwas further dried to a residual solvent amount less than 0.1 wt %,thereby obtaining a cellulose acetate film (T1). The cellulose acylateemployed had Tg of 140° C.

The prepared film was passed through induction heated rolls of atemperature of 60° C. to elevate the film surface temperature to 40° C.,then coated with an alkali solution of a following composition in anamount of 14 ml/m² by a bar coater, then made to stay for 10 secondsunder a steam-type far infrared heater (manufactured by NoritakeCompany) heated at 110° C., and was further coated with purified waterin an amount of 3 ml/m² by a bar coater. In this state, the film had atemperature of 40° C. It was then subjected to a water rinsing by afountain coater and a water removal by an air-knife, repeated 3 cycles,and was dried by staying in a drying zone of 70° C. for 2 seconds. Inthis manner the surface of the cellulose acetate film was subjected to asaponification treatment.

(Composition of Alkali Solution)

potassium hydroxide  4.7 parts by weight water 15.7 parts by weightisopropanol 64.8 parts by weight propylene glycol 14.9 parts by weightC₁₆H₃₃O(CH₂CH₂O)₁₀H (surfactant) 1.0 part by weight

The obtained cellulose acetate film T1 had a width of 1340 mm and athickness of 88 μm. An auto birefringence meter KOBRA 21ADH(manufactured by Oji Scientific Instruments Ltd.) was used to measurethe optical characteristics of the prepared cellulose acetate film (T1).At 590 nm, the in-plane retardation (Re) was 60 nm, and the retardationin thickness direction (Rth) was 190 nm. In the optically anisotropiclayer, an average direction of the phase retarding axis wassubstantially perpendicular to the longitudinal direction of the film.

On a saponified surface of thus prepared continuous web celluloseacetate film (T1), an alignment film coating liquid of a followingcomposition was continuously coated with a wired bar of #14. Analignment film was formed by drying with a warm air of 60° C. for 60seconds and with a warm air of 100° C. for 120 seconds.

(Composition of alignment film coating liquid)  10 parts by weightfollowing denatured polyvinyl alcohol water 371 parts by weight methanol119 parts by weight glutaraldehyde  0.5 parts by weight Denaturedpolyvinyl alcohol

A coating liquid of a following composition, containing a rod-shapedliquid crystal compound, was continuously coated with a wired bar of#5.0 on the prepared alignment film. The film was conveyed at a speed of20 m/min. The solvent was removed in a step of continuously heating fromthe room temperature to 80° C., and a heating was then conducted in adrying zone of 80° C. for 90 seconds thereby aligning the rod-shapedliquid crystal compound. Subsequently, the film was maintained at atemperature of 60° C., and the alignment of the liquid crystal compoundwas fixed by a UV irradiation to obtain an optically anisotropic layerB1. Subsequently, the prepared film was immersed in a 1.5 rnol/L aqueoussolution of sodium hydroxide of 55° C. for 2 minutes, and then wasimmersed in water to sufficiently wash off sodium hydroxide. Then it wasimmersed in a 5 mmol/L aqueous solution of sulfuric acid of 35° C. for 1minute, and then was immersed in water to sufficiently wash off thedilute aqueous solution of sulfuric acid. Finally, the sample wassufficiently dried at 120° C. In this manner an optical compensationfilm 5-A, in which an optically anisotropic layer B1 was laminated onthe cellulose acetate film T1, was prepared.

(Composition of Coating Liquid Containing Rod-Shaped Liquid CrystalCompound)

(Composition of coating liquid containing rod-shaped liquid crystalcompound) 100 parts by weight following rod-shaped liquid crystalcompound (I) photopolymerization initiator  3 parts by weight (Irgacure907 manufactured by Ciba-Geigy Ltd.) sensitizer (Kayacure DETX,manufactured by  1 part by weight Nippon Kayaku Co.) followingfluorinated polymer  0.4 parts by weight following pyridinium salt  1part by weight methyl ethyl ketone 172 parts by weight Rod-shaped liquidcrystal compound (I)

Fluorinated polymer

Pyridinium salt

From the prepared optical compensation film 5-A, the opticallyanisotropic layer B1 alone, containing the rod-shaped liquid crystalcompound, was peeled off and subjected to a measurement of opticalcharacteristics with an auto birefringence meter KOBRA 21ADH(manufactured by Oji Scientific Instruments Ltd.). In a measurement at590 nm, the optically anisotropic layer B1 alone had Re of 0 nm and Rthof −260 nm. It was also confirmed that an optically anisotropic layer,in which the rod-shaped liquid crystal molecules were substantiallyvertically aligned to the film surface, was formed.

(Preparation of Optical Compensation Film 5-B)

Heat-shrinkable films were adhered, by acrylic tacky adhesive layers, onboth surfaces of a polycarbonate film, which was then stretched with astretching apparatus under heating to cause shrinkage of theheat-shrinkable films, and the heat-shrinkable films were then peeledoff. In this manner an optical compensation film 5-B was prepared withRe of 268 nm, Rth of 1 nm and a thickness of 60 μm.

(Preparation of Optical Compensation Film 5-C)

Heat-shrinkable films were adhered, by acrylic tacky adhesive layers, onboth surfaces of an Arton film (manufactured by JSR Corp.), which wasthen stretched with a stretching apparatus under heating to causeshrinkage of the heat-shrinkable films, and the heat-shrinkable filmswere then peeled off. In this manner an optical compensation film 5-Cwas prepared with Re of 195 nm, Rth of −20 nm and a thickness of 135 μm.

(Preparation of Optical Compensation Film 5-D)

An Arton film (manufactured by JSR Corp.) was monoaxially stretched toobtain a film Al with Re of 170 nm, Rth of 85 nm and a thickness of 70μm.

A surface of the Arton film A1 was subjected to a corona treatment, andan alignment film was formed thereon in the same manner as describedabove. Then an optically anisotropic layer B2 was formed with a coatingliquid containing the aforementioned rod-shaped liquid crystal compound.The optically anisotropic layer B2 alone had Re of 0 nm and Rth of −135nm. It was also confirmed that an optically anisotropic layer, in whichthe rod-shaped liquid crystal molecules were substantially verticallyaligned to the film surface, was formed. In this manner an opticalcompensation film 5-D, in which an optically anisotropic layer B2 waslaminated on the Arton film Al, was prepared.

(Preparation of Polarizing Plate 5-A)

A polarizing film was prepared in the same manner as in Example 9. Asurface of the prepared optical compensation film 5-A, not bearing theoptically anisotropic layer B1 (namely a rear surface of the celluloseacetate film T1) was adhered to a surface of this polarizing film, whilea cellulose triacetate film (FUJITAC TD80UL, manufactured by Fuji PhotoFilm Co.) having a saponified surface was adhered to the other surface,with a polyvinyl alcohol-based adhesive, whereby a polarizing plate 5-Awas prepared. In this operation, the absorbing axis of the polarizingfilm and the phase retarding axis of the cellulose acetate film T1 weremade perpendicular each other.

(Preparation of Polarizing Plate 5-B)

The optical compensation film 5-B prepared above and the polarizingplate 104 of Example 9 were adhered with an acrylic tacky adhesive. Inthis operation, the absorbing axis of the polarizing film and the phaseretarding axis of the optical compensation film 5-B were made paralleleach other. In this manner a polarizing plate 5-B with an opticalcompensation film was prepared.

(Preparation of Polarizing Plate 5-C)

A polarizing film was prepared in the same manner as in Example 9. Onboth surfaces of the polarizing film, cellulose triacetate films(FUJITAC T40UZ, manufactured by Fuji Photo Film Co., Re=1 mm, Rth=35 nm,thickness 40 μm) having a saponified surface were adhered with apolyvinyl alcohol-based adhesive, whereby a polarizing plate 301 wasprepared.

The optical compensation film 5-C prepared above and the polarizingplate 301 were adhered with an acrylic tacky adhesive. In thisoperation, the absorbing axis of the polarizing film and the phaseretarding axis of the optical compensation film 5-C were madeperpendicular each other. In this manner a polarizing plate 5-C with anoptical compensation film was prepared.

(Preparation of Polarizing Plate 5-D)

The optical compensation film 5-D prepared above and the polarizingplate 301 were adhered with an acrylic tacky adhesive. In thisoperation, the optically anisotropic layer B2 contained in the opticalcompensation film 5-D was positioned at the side of the polarizing plate301, and the absorbing axis of the polarizing film and the phaseretarding axis of the optical compensation film 5-D were made paralleleach other. In this manner a polarizing plate 5-D with an opticalcompensation film was prepared.

(Mounting Evaluation on IPS Panel)

Evaluation of mounting on an IPS panel was conducted in following fourclasses A to D, according to the type of the optical characteristics ofthe optical compensation film employed on the liquid crystal display.

(Class A)

In a structure shown in FIG. 5, there were employed the polarizing plate5-A as an optical compensation film 4 and a polarizing plate 1, an IPSliquid crystal cell as a liquid crystal cell 3, and the polarizing plate104 prepared in Example 9 as an optical film 5 and a polarizing plate 2,and these were adhered with a tacky adhesive material. The adhesion wasmade in such a manner that the optical compensation film 5-A of thepolarizing plate 5-A was positioned at the side of the liquid crystalcell, and that the optical film 004 of the polarizing plate 104 waspositioned at the side of the liquid crystal cell. The absorbing axes ofthe upper and lower polarizing plates were made perpendicular eachother, and the absorbing axis of the lower polarizing plate was madeperpendicular to the direction of the molecular longer axis of theliquid crystal cell (namely the phase retarding axis of the opticalcompensation film 5-A being parallel to the direction of molecularlonger axis of the liquid crystal cell). A liquid crystal cell was takenout from a liquid crystal television TH-32LX500 (manufactured byMatsushita Electric Industrial Co.), and was used as the liquid crystalcell 3, after removing the polarizing plates provided at the observingside and at the backlight side, and the optical film. In this liquidcrystal cell, the liquid crystal molecules were substantially parallelaligned between the glass substrates in a state without voltageapplication and in a black display state, with a phase retarding axisparallel to the imaging surface. Also a mounting was executed with asimilar layered structure, employing each of the polarizing platesutilizing the optical films of Comparative Example 1, 2, obtained inExample 9, instead of the optical film of the invention.

(Class B)

In a structure shown in FIG. 5, there were employed the polarizing plate5-B as an Optical compensation film 4 and a polarizing plate 1, the IPSliquid crystal cell as a liquid crystal cell 3, and the polarizing plate104 prepared in Example 9 as an optical film 5 and a polarizing plate 2,and these were adhered with a tacky adhesive material. The adhesion wasmade in such a manner that the optical compensation film 5-B of thepolarizing plate 5-B was positioned at the side of the liquid crystalcell, and that the optical film 004 of the polarizing plate 104 waspositioned at the side of the liquid crystal cell. The absorbing axes ofthe upper and lower polarizing plates were made perpendicular eachother, and the absorbing axis of the lower polarizing plate was madeperpendicular to the direction of the molecular longer axis of theliquid crystal cell (namely the phase retarding axis of the opticalcompensation film 5-B being perpendicular to the direction of molecularlonger axis of the liquid crystal cell). The liquid crystal cellemployed was a parallel alignment cell, same as in the class A. Also amounting was executed with a similar layered structure, employing eachof polarizing plates utilizing the optical films of Comparative Example1, 2, obtained in Example 9, instead of the optical film of theinvention.

(Class C)

In a structure shown in FIG. 5, there were employed the polarizing plate5-C as an optical compensation film 4 and a polarizing plate 1, the IPSliquid crystal cell as a liquid crystal cell 3, and the polarizing plate104 prepared in Example 9 as an optical film 5 and a polarizing plate 2,and these were adhered with a tacky adhesive material. The adhesion wasmade in such a manner that the optical compensation film 5-C of thepolarizing plate 5-C was positioned at the side of the liquid crystalcell, and that the optical film 004 of the polarizing plate 104 waspositioned at the side of the liquid crystal cell. The absorbing axes ofthe upper and lower polarizing plates were made perpendicular eachother, and the absorbing axis of the lower polarizing plate was madeperpendicular to the direction of the molecular longer axis of theliquid crystal cell (namely the phase retarding axis of the opticalcompensation film 5-C being parallel to the direction of molecularlonger axis of the liquid crystal cell). The liquid crystal cellemployed was a parallel alignment cell, same as in the class A. Also amounting was executed with a similar layered structure, employing eachof the polarizing plates utilizing the optical films of ComparativeExample 1, 2, obtained in Example 9, instead of the optical film of theinvention.

(Class D)

In a structure shown in FIG. 5, there were employed the polarizing plate5-D as an optical compensation film 4 and a polarizing plate 1, the IPSliquid crystal cell as a liquid crystal cell 3, and the polarizing plate104 prepared in Example 9 as an optical film 5 and a polarizing plate 2,and these were adhered with a tacky adhesive material. The adhesion wasmade in such a manner that the optical compensation film 5-D of thepolarizing plate 5-D was positioned at the side of the liquid crystalcell, and that the optical film 004 of the polarizing plate 104 waspositioned at the side of the liquid crystal cell. The absorbing axes ofthe upper and lower polarizing plates were made perpendicular eachother, and the absorbing axis of the lower polarizing plate was madeperpendicular to the direction of the molecular longer axis of theliquid crystal cell (namely the phase retarding axis of the opticalcompensation film 5-D being perpendicular to the direction of molecularlonger axis of the liquid crystal cell). The liquid crystal cellemployed was a parallel alignment cell, same as in the class A. Also amounting was executed with a similar layered structure, employing eachof the polarizing plates utilizing the optical films of ComparativeExample 1, 2, obtained in Example 9, instead of the optical film of theinvention.

In the liquid crystal display thus prepared, a light leak rate and acolor shift in a black display state were evaluated in a direction withan azimuthal angle of 45° and a polar angle of 60° from the frontaldirection to the apparatus. Results are shown in Table 4. The liquidcrystal displays employing the polarizing plate 104 utilizing theoptical films of the invention showed no color shift and little lightleakage when observed from an inclined direction, while the liquidcrystal displays employing the polarizing plates utilizing ComparativeExamples 1, 2 showed a large color shift and a large light leakage.

Example 13

(Evaluation of Mounting on OCB Panel)

The optical film 001 of the invention obtained in Example 1 wasevaluated utilizing a liquid crystal display described in Example 1 ofJP-A-10-48420, an optically anisotropic layer containing discotic liquidcrystal molecules described in Example 1 of JP-A-9-26572, an alignmentfilm formed by coating polyvinyl alcohol, and an OCB-mode liquid crystaldisplay described in FIGS. 10 to 15 of JP-A-2000-154261, and provided asaisfactory performance in the viewing angle-dependent contrast, and asatisfactory result was obtained in the color shift in an evaluation asin Example 10. The optical films of Comparative Examples 1, 2 wereinferior, in a similar evaluation, to those of the invention. Theseresults are shown in Table 4.

As explained in the foregoing, the optical film of the invention, andthe optical compensation film and the polarizing plate utilizing thesame are identified as an optical film which is capable of suppressing acolor shift and providing a high contrast ratio over a wide viewingangle.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the described embodiments ofthe invention without departing from the spirit or scope of theinvention. Thus, it is intended that the invention cover allmodifications and variations of this invention consistent with the scopeof the appended claims and their equivalents.

The present application claims foreign priority based on Japanese PatentApplication Nos. JP2005-262304 and JP2006-63026, filed Sep. 9 of 2005and Mar. 8 of 2006, respectively, the contents of which are incorporatedherein by reference.

1. An optical film having retardations satisfying relations (1) to (3):0≦Re(550)≦5;  (1)−15≦Rth(550)≦15; and  (2)||I|+|II|+|III|+|IV|>0.5 (nm),  (3) with definitions: I=Re(450)-Re(550); II=Re(650)-Re(550); III=Rth(450)-Rth(550); andIV=Rth(650)-Rth(550), wherein Re(450), Re(550) and Re(650) are in-planeretardations measured with lights of wavelength of 450, 550 and 650 nm,respectively; and Rth(450), Rth(550) and Rth(650) are retardations in athickness direction of the optical film, which are measured with lightsof wavelength of 450, 550 and 650 mn, respectively, and wherein I, II,III and IV satisfy relations (4-A) to (7-A):−50≦I≦0;  (4-A)0≦II≦50;  (5-A)−50≦III<0; and  (6-A)0<IV≦50,  (7-A) wherein a material for forming the optical filmcomprises at least one resin selected from an acrylic polymer, astyrenic polymer, and cellulose acylate.
 2. The optical film accordingto claim 1, wherein −15≦Rth(550)≦0.5.
 3. The optical film according toclaim 1, wherein the optical film is stretched.
 4. The optical filmaccording to claim 1, wherein the optical film has a thickness of from20 to 200 μm.
 5. The optical film according to claim 1, wherein theoptical film has a spectral transmittance, at a wavelength of 350 nm, of10% or less.
 6. The optical film according to claim 1, wherein theoptical film has a spectral transmittance, at a wavelength of 380 nm, of45 to 95%.
 7. The optical film according to claim 1, wherein thematerial for forming the optical film is cellulose acylate.
 8. Theoptical film according to claim 1, wherein the cellulose acylate has anacyl substituent, the acyl substituent is substantially only an acetylgroup, and a total substitution degree of the acyl substituent is from2.56 to 3.00.
 9. A polarizing plate comprising: a polarizer; and anoptical film according to claim
 1. 10. A liquid crystal displaycomprising: a substrate; the optical film according to claim 1; and aliquid crystal cell containing liquid crystal molecules aligned to besubstantially parallel to the substrate in a black display state of theliquid crystal display.